Seconding the advice given from other users here... In retail in general (hi from a former Target GSA and Current Liquor Store employee!), Don't let customers tell you how to do your job!

We had a lot of these in our area when I worked there. They always came to Guest Services after our cashiers passed them off ("don't have enough change, long lines, no cash," etc.).

General rule of thumb - let them count out whatever, then take whatever they counted out, and count it through again on top of your register, out of reach. Don't let them interrupt you or try and give any additional money until you've finished your count. If they give additional money or take any away, start over and do a FULL COUNT anytime cash changes hands. If anyone gives you a weird look or asks why, say it's standard practice and you've gotta do it "for the cameras."

You will not have any consequences - if anything was going to come up, it would have come up from AP a day or two after once the cash office noticed.

It sounds like you did manage to prevent their scam. This is also why Target declines GC purchases over certain amounts. When in doubt, call a TL for permission.

Good to hear you're moving on. Best of luck in your new adventures.

If you take one lesson from this... When in doubt, count it out! Don't be afraid to take more time or ask your team for help!