The only reason that you should be charged anything, is if they find a bad part that they missed the first time. I would be looking for something wrong in the following, bad belt guide, wrong belt, or bad pulley. The only other reason that I have seen belts come off, is a branch, mulch or stick gets between the belt and pulley. Finally which mower brand would I buy? Toro. There is no mower that will please you, if after a years use of working fine, the first problem that occurs, you're going to trash the brand. Yes, I am a Toro guy and work on them everyday.