The first Shopify app that enforces product-level purchase restrictions at checkout
“This product is for new customers only.” Now you can actually enforce that.
Your trial box, intro offer, or welcome product should only be bought once. OfferGuard matches five identity signals (email, phone, address, IP, device) against your order history at checkout to decide if someone is really new. It works at guest checkout, where Shopify has no way to tell who they are.
Free plan, no credit card. Takes about two minutes. Adds under 50ms to checkout.
Your “new customers only” product? Returning customers are buying it.
Guest checkout has no login. A customer changes their email, checks out as a guest, and buys your intro offer or trial box again. Shopify doesn't stop them.
[email protected]Plus alias[email protected]Dot trick[email protected]Throwaway emailGuest checkoutNo login at allShopify sees four new customers. OfferGuard sees one person, four times.
A web pixel starts tracking devices from the first page view. By the time they reach checkout, OfferGuard already knows their device, even if they switched emails and went incognito.
How OfferGuard catches repeat buyers
Eight checks run across every checkout. Page-level tracking starts before the customer even reaches the cart.
Email normalization
Strips dots and +aliases from Gmail. [email protected] resolves to [email protected].
Guest checkout protection
Works without a login. Shopify's limits need an account. Most buyers don't have one.
Throwaway email blocking
Rejects emails from tempmail, guerrillamail, and 3,000+ disposable providers.
Address matching
Fuzzy-matches addresses. "123 Main Street Apt 4B" and "123 Main St #4B" are the same place.
Device fingerprinting
Tracks screen resolution, timezone, hardware profile, and a persistent visitor cookie across sessions. New email, same device? Caught.
IP tracking
Counts how many different emails check out from the same IP. Three new emails from one IP in a week is one person.
Persistent visitor ID
A cookie set on first visit that survives email changes, guest checkouts, and cleared history. The strongest single signal.
Visible in Shopify admin
When a checkout is blocked, the exact check that caught it shows up in your admin. No guessing.
5
identity signals checked per checkout
<50ms
added to checkout
3,000+
disposable email providers blocked
Runs on Shopify's official Checkout Extensions API. Works on every Shopify plan.
Block 2-3 repeat orders and it pays for itself.
No contracts. No per-order fees. Cancel anytime.
Watchdog
- 1 rule
- 50 checks/month
- Email detection
- Disposable email blocking
No credit card required
Sentinel
- Unlimited rules
- Unlimited checks
- All 5 detection signals
- Post-purchase automation
- Shopify admin integration
No credit card required
Fortress
- Everything in Sentinel
- Priority support
- Advanced analytics
- Custom integrations
- Dedicated onboarding
No credit card required
Common questions
Short answers. The free plan takes two minutes and never expires.
You probably have repeat buyers right now. The free plan shows you.
Install it, set up one rule, and see what happens at your next checkout. Most merchants are surprised by what they find.
No credit card. No code changes. Cancel anytime.