I have a lot of experience in running registers. I've never fallen for this scam. I can't remember all the times it was attempted on me because it was easily over 50 times. Many times they would physically pat the counter and say "count it out right here." (It's a huge red flag if they ever tell you how to do your job in any capacity) If they ever changed the amount of money they wanted back, wanted change or told me where to count it out, I put all the money back in the register and gave them back their initial bill. I would state "You decide how you want the money back and I assure you, you will get the right amount back." This completely disables them.

Of course, I look significantly younger than I actually am, so when I did run registers I always looked like I was a teenager regardless of being in my 20s (now that I'm in my mid-thirties people still think I look early 20s). I was not inexperienced, prone to being manipulated or prone to make mistakes. Scammers and thieves commonly tried to use stolen credit cards or some other scam only to be thwarted by my attention to detail. It was probably a good thing for the businesses I worked for, because there were less experienced cashiers they could have targeted but they targeted me and lost their little gamble.