As I have stated in a number of previous threads, IMO If you buy a used deck I would only buy one of the following 4 motor Sonys decks period:
Sony PCM-R500, R700, 7010, 7030, 7050, 7040, 2600, 2800
Sony DTC-A8, A9
The best by far is the 7040 but it will not playback 32Khz or LP tapes - it has advanced error correction with a large 1MB buffer and reads through tapes the others won't
I presently own a Panasonic SV-4100, Sony PCM-R700, a Sony PCM-7040 and 8 or so SGI SDT-9000 DDS3 drives
I have owned D8, DA-P1, SV-3800, Fostex D-5 - I have never regretted selling these
I always go the DDS route first and if I get errors go to the PCM-7040 for 44.1/48 Khz tapes or the R700 for 32Khz or LP tapes - I only have kept the SV-4100 as it's the only deck I bought new
All of the decks I own I can easily repair myself as well - The 4100 is a little harder then the Sony's but not much - The 7040 uses a Sony DDS drive transport so you can easily find replacement parts as well (except the heads and boards)
Most decks ebay that are listed as having issues probably only need the pinch roller replaced (which is a $20-30 part) - When a pinch roller goes appropriate preasure is lost across the capstan motor causing the tape to slip (possibly leading to the eating of a tape - if bad enough) - They are rubber and will eventually fail over time - I have replaced these on all my decks over the years.
It is hard to tell who is selling a good deal or not but on the Sony R500, R700, 70x0 series you can have the seller give you the head hour counter to give you a good idea of how much use the deck has on it.