I dont like not being able to see stuff before I buy, but you gotta do what you gotta do for certain things that just are not going to turn up in the bins anytime soon if at all. I prefer internet sources for newer reissues, Acoustic sounds has the best packaging, but I've used them all over the years- music direct, elusive disc, Better records.
For previously owned UK pressings and other more rare or sealed items I prefer ebay sources that are really dealers or recognizably part of the vinyl community, not some guy with no turntable grabing stuff at his local used store without even looking at it and putting it on ebay becasue he thinks he has gold on his hands (which is getting more and more common and one of the reasons the stores are "dry" frequently). Once in awhile go out on a limb and buy a record listed along side jewlrey, bobleheads and baseball cards.
I do not use Gemm. "overgrading' happened on all items I got there. Record Grading is so reliant on lighting, honesty, and subjectivity- that's why I prefer to do it myself.