Technics decks were decent back in the day, though not in the same league as Nakamichi or Tandberg. They were more in tune with the mass-market manufactured cassette deck league. Having said that, Technics decks were well regarded for their reliability and performance. If the deck has been well maintained and has not been run heavily, and cosmetically/functionally in pristine condition, its a simple buying decision. The problem is that ownership history is not always available.
Spares for Japanese decks can be hard to come by if you want original replacements. Ebay is a common source for Technics pinch rollers and belts. However since Japanese deck mechanisms were quite often duplicated by Indian manufacturers, you are likely to find local varieties of replacement parts in your friendly neighbourhood electronics store. But I must say that these Indian spares are close to junk when it comes to performance and you have to be extremely lucky to a good working spare part.