For new pressings, I frequent MusicDirect, Elusive Disc, and Acoustic Sounds. I will only buy MOFI from MusicDirect and only buy Analogue Productions from Acoustic Sounds, as each are the respective manufacturers as well. If there is a problem, returns aren't an issue. I have found that if a MOFI disc is defective, MusicDirect will frequently just send a replacement disc without having to go through the return process. I will send a photo of the defect and that is usually enough. The same is true with Analogue Productions and Acoustic sounds. If you buy a defective MOFI from AP, you will certainly have to return the entire package, but they will make it right.
Discogs is my vendor of choice for used vinyl. If you know the exact pressing you want-(hint-not all pressing plants are created equal. There can be a significant sound quality difference between plants on a given release)-it can be easily found on the website. I will also check from time to time to see if my favorite CD only releases have been remastered to vinyl. Lot's of stuff in Europe that we don't see here in the states. I only buy mint, or near mint, and choose the sellers carefully as some sellers are less than stellar with grading. The sellers are star ranked and their volume of sales is also listed. I used to buy from Ebay, but you cannot verify deadwax indices and the grading was awful.