I have a few things to say. Some good. Some not.
I'm glad you quit because no one should have to put up with the craziness of LOD's and Tl's who don't back you up or explain why they are reprimanding. And the thought of an adult being reprimanded by an adult is insulting.
Sad that you didn't give it the 24 hour cool down period before you quit, so that you could have been the one in control, as in having a new job to go to in order to pay the bills.
As a new cashier. They probably saw that you had half a brain and were able to explain to newer cashiers what to do.
Also probably the same reason you were working in guest services. Sometimes that isn't a step up position. Many people are hired to work there from the get go. Sometimes not a good choice, sometimes yes a good choice.
The etl who was praising you may have a positive personality, not saying you didn't deserve it, but they may be telling all tm's that they are doing great.
As a gsa, I always made sure I thanked every cashier, cart attendant and every TM I had contact with each day. No one needs to hear negatives all the time.
Some Tl's and etl's don't see it that way and want to point out faults. A person can suck it up or walk away. It's their option of what they want to do.
Your idea of being a great employee and targets idea could be two different things. I had a cashier who thought she was gods gift to the world. And though she did get some compliments from guests, she was slow as hell, didn't play well with others and liked to kiss mgmt ass. Everyone was happy when she left.
As far as the 50¢ Price difference, I would have done the return and politely asked the guest if she remembered where the sign was so that you could have someone on the floor check out the problem. I never would have said to a guest that it's her prerogative to write a letter. Of course it is. She can do what she wants. If someone said that to me, it would twist my insides and I would tell them - you're damn straight it's my prerogative and I'd be adding that you have a flippant attitude in my letter.
So, all that being said - I wish you much luck in your new life away from target.