I am trying to ascribe blame here. I just sold one of these (actually a 564) which was working fine when I sold it. It seems to have been working fine (and I'll bet the buyer was wearing it) for a few weeks thereafter. Then the buyer reported some stem problem. He took it into some country-bumpkin repairer and suddenly it had what the repairer reports as a "gate" problem which on minor dissembly to inspect, he can't fix. So I am trying to figure out what is wrong. I NEVER assume the buyer is at fault.
But there again, about a month ago I was at a show and came across a very young and enthusiastic newbie with good taste who bought from me
very inexpensively an extraordinarily beautiful porcelain dialed 1920s Omega as a wearer.
But the crystal came off. He then got scared. So I used proper crystal glue to get it back on. About an hour later, he demanded his money back after that crystal came off again! So I assumed it had shrunk, wouldn't go back on, and gave this teenager his money back. Yet i put it in an envelope and took it home, and when I looked at it again a day later, the crystal was stuck fast!
In retrospect, he had clearly, without knowing what he was doing, picked at the crystal and torn it out of the case before the glue had dried and then nervously professed a lack of confidence in the whole watch!!
So the buyer, - even with good taste, - IS sometimes at fault.