I'm not a luthier but I've seen a few old guitars ... certainly ask and get a straight answer, that all six of the tuners turn 360 degrees happily. If that is the same guitar you are interested in (and not a stock picture) it looks little used, but the tuner gears can get worn with use over time, especially the 6th string if its a fairly advanced player, and usually that would mean replacing the whole set of tuners if even one of them refuses to work.
Another thing to add re the frets, ask and get a clear answer that if you rub your hand pressing along the side of the neck where the frets come to the edge, that none of the frets stick out.
I would ask for pictures of the back and sides of the guitar, and get a clear assurance that there are no cracks in any of the woodwork joins, especially where the neck joins the body, and around the headstock.
Is it a private seller or a shop? Will they accept a return if there is a problem? Certainly, Yamaha tend to make well built, reliable instruments, if at that kind of age you are wise to ask questions about it.
Simon Ambridge Series 40 (2005)
Trevor Semple Series 88 (1992)
Louis Panormo (1838)
Alexander Batov Baroque Guitar (2013)