I have been to auctions where they say they run good, but don't start them. Like everyone else, I'm skeptical then.
I was looking at a really beat Deere 214 once at an auction and they were getting close. Out of curiosity, I reached over and turned the key..it started right up and ran fine! That was a shock. I also had managed to cause it to sell very well, I think it went for like $250..probably at least $100 more than it would have if not started.
It works the other way too...
I was at a different auction (A huge one in Okawville that normally brings 1,000+ bidders ..but I got my kwik way loader there for $300 so you never know) Anyway, they had a very nice looking Deere 314 that I was thinking of buying to resell. They started it up and it knocked so loud everyone turned to stare. They even revved it up! (I was sure something was going to fly out)
It sold to some older guy for something like $1200! While I was loading the stuff I did buy, he was over there trying to restart it, and it would only backfire. Not that it needed to ever run again before being overhauled.
That is why I won't bid on a non running "runs great" tractor without figuring it doesn't run great.