It’s becoming an organized crime tactic:

Card draining is when criminals remove gift cards from a store display, open them in a separate location, and either record the card numbers and PINs or replace them with a new barcode. The crooks then repair the packaging, return to a store and place the cards back on a rack. When a customer unwittingly selects and loads money onto a tampered card, the criminal is able to access the card online and steal the balance.

[…]

In card draining, the runners assist with removing, tampering and restocking of gift cards, according to court documents and investigators.

A single runner driving from store to store can swipe or return thousands of tampered cards to racks in a short time. “What they do is they just fly into the city and they get a rental car and they just hit every big-box location that they can find along a corridor off an interstate,” said Parks.