
Quoting
Mr. Knowitall
Are we to infer that this investigator works for the store, then? And by "don't go to the store", do you mean you've been banned from the store (If so, don't go to the store) or was that just in relation to whether there would be a check to pick up?
That's a very reasonable conclusion.
Perhaps they were suspicious the first time, and their suspicions only grew with your subsequent conduct and exchange. The only way to know what they were thinking, or when, is from them.
Nobody framed you for anything.
I can't see the letter from here. If you have in fact been banned from the store, yes, it's a good thing you didn't go in the event that somebody might have thought you were violating the ban. As you didn't go to the store, we'll never know what might have happened.
There's no law that says a store employee can't suspect you of shoplifting, or that a store employee has to be nice to you. There's no law that requires an employee to process your return herself if her suspicions or store policy cause her to instead request that a manager take over. You have not indicated what in her actions would have "humiliated" you, or that your humiliation would have been apparent to any other person. You have not indicated that you have suffered any damages, economic or otherwise, as a result of this claimed humiliation. So, so far, you haven't shared anything with us that would support a successful lawsuit.
You have told us that there is no proof for them to find. If that's the case, then it should follow that they are suspicious of your conduct.
You never have to talk to a store employee. You have a Fifth Amendment right not to talk to the police. If you don't talk to the store employee, you can reasonably anticipate that any ban from the store will continue and that you're probably not going to get a gift card or check. But odds are the purpose of the interview is to try to get you to confess to criminal activity, and there are plenty of reasons not to put yourself in that position.