you need to be very careful with used ohlins shock prices... they have multiple versions of the ttx, and the older non GP units are a great shock but, people try to get new gp 2 or 3 pricing out of them, when they are clearly not the latest and greatest technology.
oh, and NEVER BELEIVE THE SHOCK WAS "JUST" SERVICED, WITHOUT FULL DOCUMENTATION, FROM A REPUTABLE SHOCK SERVICER. the sellers "always say that, it was refreshed", then you find out different when opening the box.
Personally, unless it was close to 50% off retail or better, I wouldn't entertain used, especially if it is not a gp 2 or better. you will still need to service it for piece of mind, and more than likely need the correct spring for your bike, weight, and track/street specification.
your results may vary. Ski
May we all, get to have a chance to ride the fast one, walk away wiser when we crash one, keep hopin that the best one is the last one.