If he was lowering the boom and the peddle stuck he may have put the spool into the dentented, float, position. If he doesn't use that position very often it might have stuck in that position. I had one awhile back where that happened to a customer and he had absolutely no control of the boom with that peddle. I had to use a pry bar to get the spool untsuck, and then pull the detent mechanism and clean/free it up for him so it didn't happen again. That said if he kicked the peddle too hard he may have also broken, or bent, a part of the linkage causing the funtion not to work.
In any case, based on what your saying happened, I think the guy made an assumption on the problem and then began taking things apart without every doing any real troubleshooting (nothing uncommon in my experience). That being the case, I'd say the probility of the pump actually being bad are really slim. Good luck and hope it turn out to be a good machine if you wind up buying it.