There's a lot of factors that go into asking for a letter, and whether or not you have an A isn't always the best guideline. I'd ask to get a feel for his/her level of enthusiasm for me as a pre-med student. The best way to avoid a cookie cutter letter IMO though is to interact with the professor (ask questions, etc.) or submit your personal statement and CV.
I would not trust what you hear, most people waive the right to see their letters because med schools believe them to be more honest opinions that way. So what're the chances that several students saw their letters from that same professors and then compared them?