Sportlots: do alot of purchases through them, but like others have said I kind of narrow my purchases to a few sellers.
ebay: still purchase but very selective
amazon: purhcased boxes and supplies
dacardworld: boxes but not for a while
bcwsupplies (for supplies, obviously), once or twice
comc: a few purchases but forget about this site often. Have thought about selling
justcommons: never been
craigslist: couple of purchases
facebook marketplace: couple of lots or binders of cards
armchair: Massive inventory of hockey cards covering all minor pro and major junior leagues
ACHL - AHL - BCHL - CHL - CoHL - ECHL - IHL - LNAH - MHL - NCAA - NHL - OHL - QMJHL - QSMHL - QSPHL - RHI - SPHL - UHL - USHL - WCHL - WHL - WPHL
Use this site to find one card for my Ultimate Hockey Card Catalog. Great for finding oddball hockey or minor sets. I use the on sale section to purchase that one card to add to my catalog. Great site for the Hockey collector.
LCS: I get my supplies there, can not beat it, bought 4 each 5000ct monster boxes for $ 14.00
Finally TCDB, if I ever get arond to completely organizing my collections and start doing trades.
Trying to acquire one card for every for every set, insert, parralle, minor, euro, team issue, oddball etc sets produced for Hockey. Been an interesting project.