Any advice on buying quality vinyl

I seek out best pressings, in my experience they are all first release pressings either in the country of origin of master tapes or Japanese from 70s, and the best condition. Within reason, I always choose better sound quality over better condition. There are exceptions when sound quality is very close and slightly worse record is in much better condition and the music recorded requires that silence be silent. In other words, I don't want any clicks or pops or even soft crackles where they have absolutely no place to be. Example is Cielo e Terra by Al Di Meola. Japanese is best, I accumulated ten copies of this album just to have one almost perfect and another a small step below it. So, I ended up with four Japanese, one Dutch and five American. It was recorded in the US, and US copy sounds pretty good but no match for Japanese, Dutch is close to US, as I remember. I would sell eight copies that I don't need if it was worth it but as things are I keep them all.

Discogs is the database for sure, but ruined by careless/dishonest/ignorant users IME. I have hardly got a satisfactory deal from them, only 5 % at most have been exactly as described, unfortunately. The biggest problem is lack of photos of actual albums in question, and that is the main source for confusion and abuse, just take a look at feedbacks ..... incredibly lots of confusion there. And no buyer protection whatsoever when ripped off.
For me personally eBay is more safe place to buy used vinyls, nevertheless. Like it has always been. Of course, you should be very very careful before you hit the button. It´s your decision, your money.

My brief experience with a very clean, shiny, new looking record, and frustration after dropping my Dynavector stylus into the groove. 
I was puzzled, not shocked (since it happens once in a while), that I was hearing crackling and a loud hiss from beginning to end!
 I removed the record, looked at it closely with my bare (not bear) eyes, and dang if I didn't see pristine, clean grooves from the outer edge to the inner. 
Note that I paid a premium for this Robert Johnson LP- maybe ten bucks.
Anyway, one day I was on call, so I decided to take the LP with me to the operating room. We use high powered Leica microscopes for neuro and spinal surgery. I slapped a 400 lens on the scope, placed the LP in position and what I saw took my back 40 years.* Throughout the entire LP, along the sides of the grooves, were straight, vertical lines. At that magnification it looked like they were one sixteenth apart. Looking closer, I could see that each line looked like a clean chisel mark, carved deep into the sidewall. Contrasting against the black, clean vinyl, the marks looked white/gray. Very uniform and consistent in size.
 *The only way this could have happened, I think (unless Michael Angelo shrunk himself and his chisel, and hates me and/or Robert Johnson) is by a bad stylus. A broken stylus with a sharp broken edge, most likely 2 broken sharp edges riding inside the groove and cutting into the sidewalls at 33.3 rpms and 26 tons (really?) of pressure, hot stamping and cutting that sumbitch- all because some teenager kid decided to place a nickel (please add 5 more tons) on top the Olympus head shell (we had an Olympus television with a record player on the side inside a drawer) so that the needle wouldn't skip and jump when he was listening to his brothers James Brown at The Apollo doing Please, Please, Please! when his brother wasn't home, of course.
 So, sometimes, cleaning your record 3,4,5 times with a VPI or Ultra, Out of this Galaxy cleaning machine, just won't help.
 But, I do strongly recommend cleaning your LPs and cleaning your stylus. And don't let your brother or sister mess with your stereo.

^ Great story, well written, ending up with an über Cleaning Machine: ) Very funny indeed ´cos you never know what lurks there inside the groove on secondhand/used/virgin records and it´s always recommended to clean your records, old and new before playing.
I use US in the end and proper rinsing and drying. Use as little chemicals as reasonably possible with US, very little alcohol and just some drops of water surface stripping agent Tetenal. At least twenty minutes in US bath.
My method is quite simple, first US with my cheap BAKU, drying the wet record with (reasonably cheap) Moth. And I always brush the stylus before each side.

Never had a good experience from Discogs yet and will not waste my time again there.
Only 1 really bad album purchased on eBay that was not as I expected or described and I got a full refund in that case.
Between eBay and my LRS I am all set for my albums.