I am a mechanic by trade, have been doing it for 15 years. I have only scratched one rim in that entire time, and I had it refinished for the customer at my own expense.
There is a nylon guide that goes on the mounting arm to prevent scratching, but the rim lip had to be clean, any dirt on there will get dragged underneath and scratch. I also apply rim lube to the lip to make sure there are no marks left.
Edit: Did not read the entire thread, but if the rims were "painted" with a spray bomb, all bets are off. A factory wheel finish is much much much more durable, unless you had them done properly by powder coating.
Last edited by MightyMouseTech; 03-09-2013 at 10:18 AM.