One discount per customer. Even at guest checkout.
Shopify sees four new customers. OfferGuard sees one person, four times. Five detection signals identify repeat buyers at guest checkout — before the discount is applied.
Free forever plan. No credit card. 2-minute setup. Under 50ms checkout latency.
Your new customer discount works great. That's the problem.
Guest checkout doesn't need a login. Nothing stops someone from coming back with a different email.
[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.
If your average discount is $15 and just 10 customers reuse it each month, that's $150/mo walking out the door.
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
Detection signals checked in parallel
<50ms
Checkout latency added
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
Questions merchants ask before installing
The short version: it works at checkout, takes 2 minutes to install, and the free plan never expires.
Your discounts are leaking revenue right now.
Install the free plan and let the data show you. Most merchants are surprised by what they find.
No credit card. No code changes. Cancel anytime.