Supplement brands get pitched by email agencies constantly, and most of those pitches are interchangeable: a revenue screenshot, a promise about flow builds, a percentage of revenue attributed to email. None of it tells you whether the agency understands the thing that actually determines whether your program works.
Know what good looks like before you take the pitch
Klaviyo publishes benchmark data drawn from more than 183,000 brands, and one figure from it is worth carrying into every agency call: flows generate roughly 41% of total email revenue from just 5.3% of sends, with revenue per recipient close to 18 times that of campaigns.
That ratio is the entire argument for scrutinizing architecture rather than output. Automated flows are the highest-leverage surface in the account by an order of magnitude, and an agency whose pitch centers on campaign calendars and send volume is proposing to spend your retainer on the lower-yield side of that split.
Supplements are a replenishment business, not a campaign business
For most ecommerce categories, retention is about giving someone a reason to come back. For supplements, the reason already exists: the customer runs out. Your job is to reach them in the window between running low and deciding not to reorder.
That window is short and it is product-specific. A 30-day supply and a 90-day supply need completely different reminder timing, and if the agency treats both with the same generic winback flow, they are guessing.
Ask directly: how would you set replenishment timing for each SKU, and what would you use to determine it? A good answer references your actual product sizes and repeat-purchase data. A weak answer describes a standard 30/60/90-day sequence.
Subscription and one-time buyers are different people
If you sell a subscription, a meaningful share of your list is already on autopilot, and sending them replenishment reminders is worse than useless. It reminds them they are paying you monthly.
The agency should be able to explain, without prompting, how they suppress subscribers from acquisition-style flows, how they handle pre-billing notices, and what they send to a subscriber who has just cancelled. Churn-save messaging is where most of the recoverable revenue in a subscription supplement business actually sits, and it is the flow most agencies never mention in a pitch.
Ask which subscription platform they have actually worked in
This is the question that separates agencies fastest, because subscription tooling is not interchangeable. The major platforms in the Shopify supplement world are Recharge, Skio, Stay.ai, and Smartrr, and each one hands Klaviyo a different set of events to build on.
What matters is not brand familiarity but event-level fluency. On Recharge, for example, the documented trigger events include subscription started, order upcoming, charge failed, order skipped, and subscription cancelled, that last one carrying the cancellation reason so a save flow can branch on why the customer left. An agency fluent in the platform talks in those terms without being prompted. An agency that is not will build you flows that either never fire or fire at the wrong people.
Useful questions:
- Which subscription events does our platform send to Klaviyo, and which ones are you planning to build on?
- How do you trigger a save sequence off a cancellation, and can you branch on the cancel reason?
- How do you handle dunning and failed payments: in the platform, in Klaviyo, or both? Who owns that messaging so customers do not get two versions of it?
- How do you keep skip and swap prompts from cannibalizing a charge that would have gone through anyway?
If you are mid-migration between platforms, say so early. Moving subscription providers reshapes your event data, and flows built against the old platform's events will quietly break. An agency that has run a migration will tell you this before you ask. One that has not will find out on your account.
Compliance is a real constraint, not a formality
The exposure here is specific and recent. In April 2023 the FTC sent Notice of Penalty Offense letters to roughly 670 companies marketing supplements and functional foods, with civil penalties that can exceed $50,000 per violation. The FTC's Health Products Compliance Guidance requires competent and reliable scientific evidence for health claims, in place before the claim runs, and it applies to email and subject lines exactly as it applies to your website.
An agency that has never had email copy reviewed against that standard will happily write you a subject line that implies a treatment claim. Ask what their review process looks like and whether they have worked with brands that have counsel reviewing marketing copy. You are not looking for legal expertise. You are looking for evidence that they know the constraint exists and have worked inside it before.
Ask to see architecture, not results
Revenue screenshots prove almost nothing. They do not show you what share was incremental, what the account looked like before, or whether the growth came from list growth rather than better email.
Instead, ask for a walkthrough of a live account's flow logic: the conditional splits, the suppression rules, the timing profiles. Two things become obvious very quickly. Whether the account is actually structured or is just a pile of flows nobody has audited in a year, and whether the person on the call built it or is reading someone else's work.
One useful probe: Klaviyo supports five distinct flow trigger types, being list, segment, metric, date property, and price drop. Most agencies build almost exclusively on metric triggers. A supplement program with a replenishment cycle and a subscription base should be using date-property and segment triggers too. If the agency has never built on anything but metric triggers, they will rebuild the same four flows every brand already has.
What the pricing model tells you
Flat monthly retainers align an agency to steady output, and mid-market retention retainers generally run $6,000 to $12,000 a month. Revenue-share models align them to sending more, which in a supplement business often means burning your list into a deliverability problem eighteen months from now.
Neither is wrong, but ask how the model handles a month where the correct answer is to send less. If there is no good answer, you have learned something.
Red flags worth walking away from
- They quote a revenue percentage they will hit before seeing your account.
- They cannot name the last deliverability problem they diagnosed and how they fixed it.
- They have never worked in your subscription platform and do not treat that as worth mentioning.
- Their onboarding does not include an audit of your existing flows and list health.
- They talk about design and copy but never about segmentation or suppression.
- They have no answer for how FTC substantiation review fits their copy process.
- The person selling you is not the person who will touch the account, and they will not tell you who is.
Five questions for the first call
- How would you time replenishment reminders for our specific SKUs, and what data would you need?
- How do you keep active subscribers out of flows meant for one-time buyers?
- Which subscription platform events would you build our save and dunning flows on?
- Which flow trigger types beyond metric triggers would you use for us, and why?
- Who is actually in the account day to day, and how often do they audit it?
Frequently asked questions
Does a Klaviyo agency need experience with my specific subscription platform?
Not necessarily with your exact platform, but they do need to have built flows off subscription event data somewhere. An agency that has only worked with one-time-purchase brands will treat your subscribers as ordinary customers, which is the single most common way supplement retention programs leak revenue.
Should we hire an agency or build the program in-house?
In-house wins when you have consistent volume and someone who owns the channel full time. An agency wins when you need the architecture built correctly once and maintained. The full decision framework, with real salary and retainer numbers, is in our in-house vs agency guide.
How long before a retention program shows results?
Flow revenue tends to move first, because flows reach people who were already going to be reachable. Campaign and list-health improvements take longer because they depend on sending behavior changing over weeks. Be skeptical of anyone promising a step change in the first month. In month one the responsible work is auditing and fixing, not sending more.
What should the first 30 days look like?
An audit of existing flows, list health, and deliverability. A map of which subscription events are actually firing into Klaviyo. A prioritized fix list. If an agency wants to start sending campaigns in week one, they are optimizing for looking busy. You can run the first version of that audit yourself with our 30-minute checklist.
How much should we expect to pay?
Cost is driven by scope more than list size: how many flows need rebuilding, whether campaigns are included, whether design and copy are in scope, and how much subscription complexity exists. Ask for the model and what is explicitly out of scope, and be wary of any quote given before someone has looked inside your account.
Sources
- Klaviyo, Email Marketing Benchmarks. Dataset of 183,000+ brands, covering flow versus campaign revenue share and revenue per recipient.
- Klaviyo Help Center, Getting started with flows. Flow trigger taxonomy.
- Recharge. Subscription event metrics as Klaviyo triggers.
- FTC. Health Products Compliance Guidance.
- FTC. Penalty offense letters to health product marketers.