Well, I do take it personally when the guest is doing something that requires my participation to get away with it, like ticket switching, coupon fraud, passing counterfeit money or doing return fraud. Sometimes, even when you, as a TM, are being a big stickler about everything you end up having to go along with something you know is hinkey because you can't come up with a solid reason to refuse the transaction, or you know it's not in your best interests to confront this person, or they are doing an excellent job of tricking you so you give them what they are asking for, but you often know (or at least suspect) as you are doing it that you are helping them steal or commit fraud. I don't like getting dragged into someone else's dirty business. Since AP TMs don't ever man registers, you may not realize that makes TMs feel.
I've actually worked as a Cashier, Electronics TM, Salesfloor TM, Inventory Prep, as well as TPS and Sr. TPS, so I've seen the "regular TM" side of things. I understand your frustration in being (seemingly) complicit in fraud and theft at the front end, but there's not a lot to be done when it's happening. The best thing to do is to alert AP during or after the transaction so they can investigate. It sucks to HAVE to allow someone to steal/commit fraud, but in the end, they never win. It may take a while, but they always get caught.
Our APs get pissed and then get pissed at the cashiers about it. I was laughing about the guest who was complaining that one of her $5 tshirts was clearance marked $2.38 and the others didn't have a clearance tag. I pointed out to her that the $2.38 clearance sticker was actually for another item, not the tshirt she was purchasing so I wouldn't honor it on the other tshirts, but I did allow the price change on the clearance stickered shirt. AP said I should have called them because she was clearly a thief.
Uh, no. I had no proof that she had changed the sticker. It could well have been a careless Guest Service team member who stuck the clearance sticker on the wrong shirt. I wasn't about to confront a guest over $2.33 that I couldn't prove.
AP went all crazy ape poop about, "Well, what if it was a $500 tv?" Yeah, then I'd probably question it. But $2.33? Vibe much?
You handled that very well (except for saying "vibe," I hate that rollout). Question it, try to get them to pay the true price, but handle with care. It's not your job to prevent theft and fraud.
About your AP team, is that TM fairly new (or just get the uniform)? Without fail, the first few months as a TPS turns people into wannabe super-cops. I always address this when I train newbies, and let them know that respect is huge in the job. Respect everyone else, and you (should) get it back.
The only things that get me upset at front-end TMs is when they make egregious errors (forgetting BOB and LISA, not calling for the GSTL/GSA if they are unsure of the policies, etc.). Otherwise, just let me know when something weird happened, and I'll look into it.