My Ebay LP buying experience has been very positive. My interest is in jazz from mostly the 50s through 70s. I could wait my entire life and never see an obscure album that I want in a used LP store, but I can go on Ebay and often find it right away. I have certainly purchased a few records where the condition was not up to the rating, but these have been surprisingly rare. I only deal with sellers with 98% or higher rating and I generally stick with US sellers just for reasonable shipping charges.
I find that I would much rather buy used records on Ebay than new records from the big mail order houses. The new records will probably have fewer ticks and pops, but the sound on the old records is nearly always superior.
As for the comment about only buying sealed records, this obviously depends on the music genre. If you want older records, they were all from the days before shrink wrap. More importantly, sealed records are often reissues, and it's just a plain fact that early issues nearly always sound better. So if you limit yourself to sealed records, you are often sacrificing sound quality.
