Customers keep reusing my welcome discount with new emails

This merchant did the sums on their own store. A $10 code on a $50 minimum order is cheap once. Repeated by one person across several accounts, on baskets far below the store’s $150 to $170 average, it is a steady leak.

What the loophole costs

The visible cost is margin: a discount on an order the store would rather not have taken at that price. The hidden cost is the customer count. Every extra account is a “new customer” in your reports, so acquisition looks better than it was and repeat rate looks worse. The same shopper is counted as several first-time buyers.

A later reply from another merchant in the thread is the line to think about. That merchant found no solution and stopped giving discount codes at all. It removes the leak and the incentive in one move, and some stores will choose it. Most want to keep a welcome offer working, so there are better questions to ask first.

How Shopify decides who is one customer

Shopify lets you limit a code to one use per customer. Its Help Center says the setting tracks a customer’s email address or phone number. A shopper who checks out with a new email and a new phone looks like a new customer to that limit.

A second thread from January 2026 asks for exactly the check this merchant wanted: validation by phone number, or by email plus phone. A reply says Shopify has no native way to do that when the discount is applied, and that Flow runs after the order, so it can tag an order for review and cannot stop the code at checkout. Our guide to how Shopify decides who is one customer covers the limit and what eligibility by segment does.

Signals worth a review

The shipping address was the common thread in this merchant’s data, and the merchant also called it imperfect. Both halves are right. A shared phone, a near-identical email or the same address and name point to one person. The same address with different names points to two people who live together.

None of these signals says why someone used a code. A shopper who forgot their account and signed up again got an offer they did not need, and they did not set out to game it. The guide on welcome discount reuse ranks the signals by strength and lists the ordinary explanations, so you can review without accusing a loyal customer.

Change the offer, not only the customer

The fixes that work best apply to everyone. This merchant already sent a generated code to each sign-up, which is the right base, and it still left room for a new email. So decide what “new customer” means for you, because the partner of an existing buyer may be exactly the new customer you want. Then review the accounts that do share details, one group at a time, with the lists below.

What MergeGuard does and does not do

MergeGuard for Shopify does not block a discount code at checkout. It works on the profiles you already have.

After the fact, the Win-back audience has a “How they shop” group with a list called Uses discounts on several profiles: regular customers who used discounts on two or more profiles. You set the minimum number of orders that makes someone a regular. A second list, Buys on sale every time, shows customers whose every order was on sale. They are lists to review, and not a verdict on anyone. The Family members list holds the relatives you marked as not duplicates, so partners and flatmates do not land in the same pile.

When a group is clearly one person, merging puts their orders on one customer, and from then on they look like the returning shopper they are. A merge is permanent, and a subscribed profile makes the merged customer subscribed, so review first. Win-back lists come with Scale and Enterprise, and other plans see the counts. MergeGuard never messages your customers.