once, i asked the non-friendly clerk/owner (hard to tell as he never volunteered anything) if they play the records before they price them and put them out: no. do you look at them before you price them and put them out: no comment and no, they don't offer any cleaning service. they recently moved and my sincere hope was that this guy did not go with them, but alas, he did.
i have had some very good finds in used records. generally jazz albums have been well cared for and i assume classical as well. 70s and 80s rock - crap shoot.

Agreed- what I look for is actual scratches or pits. If it's just smudges, grunge or dirt, it'll come out, and often reveal a pristine piece of vinyl underneath! Just got this really old looking Ahmad Jamal double LP and it sounds like it was almost never played- after removing quite the layer of dirt first.

Yeah- it's not always easy to tell, and I've gotten some real lemons along the way. But by and large, I've gotten ten times more gems, and if it's under $5 then really, the odds are pretty good.