We have had a huge problem with this too, and Ive5reached out to the AP National Investigations Center and they've given us this direction:
Per California State law, we cannot quantity limit the number of $9.99 or less gift cards people cash out. We are legally obligated to cash out as many as the "guest" wants.
However, when people come in to load a huge amount of money onto a gift card, DO NOT LOAD THEIR CARD! Load a new card and hand them that AFTER they pay. What these people are doing are having Starbucks load hundreds of dollars onto a card that they already have the numbers for, immediately transferring the money to other cards, and then having the transaction voided so they end up not paying for the hundreds of dollars they just got on their cards. If your GSTL isn't supporting you at Starbucks (which they should be), partner with your store's AP Leader and have them contact the NIC or their APBP and get specific direction from them that way you womt be hung out to dry.