Fuss, thanks. I've only bought one new one since I started shooting, and I've bought quite a few over the past three years (25?). Be careful if you haven't dealt with the seller before. What one person thinks is "excellent", or "accurate" isn't necessarily how you would define those terms. When I hear or read "accurate", I think five shot groups inside a dime at 50 yards. Some might call a quarter sized five shot group at 50 yards accurate - I call that fix it or sell it.
I'd say 90% of the time, the guns are either in very good shape, or can be easily fixed with a tune and re-seal.
There is the occasional one that looks like it was left in a damp corner in some dark basement for five years before being sold. I got one of those last year, and luckily it was a Cricket and easy to tune, rebuild and re-seal. The guy had used silicone sealer inside the gun to try and stop slow leaks... Yep, you heard that right. Broke it down to component pieces, cleaned EVERYTHING including the cocking and trigger assemblies, disassembled and rebuilt regulator, valve and transfer port, springs, scrubbed barrel and inside moderator, scrubbed stock, added pic rail and a few other items, soup to nuts. Took all morning one Saturday. Put it all back together, cleaned it up, and it was your typical Cricket tack driver with JSB Kings at 960 FPS. But that was my worst case by far. Sold it to a horse rancher in Descanso CA and he's been schwacking ground squirrels at up to 125 yards for a year now, no problems. In the seller's defense, it was VERY cheap, and came with the scope and mounts you see in the photo (Hawke Endurance).
This is the "after" picture...