Regarding the OP's initial question, "Why do some Mystery Shopping companies give you test, but don't tell you what questions you got wrong or right?"
Servimer does this, and it is primarily because of the number certification attempts that come through where a shopper has definitely not read the three-pages of guidelines. Evidence of this includes the presence of a question on the quiz that shoppers often get wrong, but where we state the correct standard early in the guidelines and add, "This is on the quiz, and is the most often incorrectly answered question." Further evidence is the dismaying number of certification attempts that come through with 47% or 54% on a test that is 21 True/False questions, with such scores clearly reflective of the shopper answering all true or all false and intending to just change whichever ones were wrong on their second attempt.
We have tried to keep the guidelines thorough yet succinct and clear, representing the process of applying for and receiving an assignment, through the on-site flow of a Servimer shop, all the way to the reporting and submitting process.
There are several evaluative criteria used by Servimer that are very different from MS standards, and we want to be sure that every shopper has a firm grip on the standards needed for them to succeed.
If anyone has any suggestions regarding our guidelines document or our certification process, I'd be very interested in learning how we can improve our material or process.
Serving as liaison between Servimer and the larger mystery shopping community. (Servimer.shopmetrics.com)