Personally I think if you're looking for higher end cards Stockx isn't a horrible idea. My budget is lower so I normally buy lower end cards off of Ebay, my LCS, Comc, and occasionaly Blowout card forums. (I'm pretty new here so I have not bought from here before)
I collect (IN NO ORDER) Pittsburgh Penguins, Pittsburgh Steelers, Vegas Golden Knights, OKC Thunder, Seattle Supersonics, Pittsburgh Pirates, Mascots, Kirby Dach, Shaq, Andrei Vasilevskiy, Henrik Lundqvist, Kobe, Landry Shamet, OBJ, Alex Iafallo, Roope Hintz, Alexandre Texier, Marvin Bagley III, Dustin Byfuglien, Denis Gurianov, D-Rose, KAT, Luke Falk, Tyrese Haliburton, Wayne Simmonds, Larry Krystowiak, Larry Fitzgerald, James Wiseman, Cam Newton, RG3, Morten Andersen, Adin Hill, Isaiah Thomas, Jameis Winston, Nene, Melo, Jaden McDaniels, Bol Bol, Recent Gonzaga Alumni, Coby White, Ai, Nickeil Alexander-Walker, Cole Anthony, Jeff Beukeboom, Kyle Busch, Kurt Busch
About 20k cards