It may well have new belts and an idler tire and the transport may function just fine. As I said about the rollers, my decks are all used and I don't know how old the rollers are, but mine appear to be in better shape then the ones in his pictures.
Wit h a 35 year old deck you can expect to have some problems unless it has been fully serviced. After all the motors develop dead spots and either slow down or stop. The pinch rollers might need replacing and no doubt unless someone has already checked the electronics my be out of whack after this long.
I don't know the going price for a fully service Pioneer 1250 but his prices seems low to me for a fully serviced deck, on the other hand his price is probably ok for a fully functioning deck with ok cosmetics and new belts and idler tires.
You have to decide what you want out of this sort of deck? I only own the ones I have because they match my silver faced Pioneer system, I don't use them for any recording and only infrequent casual playback. If you want a deck like this to be fully serviced and functional to it's best, my guess is you will spend more like 700+. An then the thing is like an old car, things will probably go wrong with it since everything is old and no longer available. If you want a superb recording deck and playback deck then I would look for either a fully serviced one from someone you can trust or a 1990's deck which would probably be a lot more reliable.
Just my two cents here.