For hockey cards in Canada I've used Grizzly Sports Cards many times https://www.grizzlysportscards.com/ . They ship fast, email you every step of the way (order received, order has been picked, tracking# etc.). They have a few other sports and non-sports cards boxes and cases but limited.
For older boxes and other sports I have used BBCE out of Indiana I think? https://bbcexchange.com/ Costs a bit more for shipping up here, but their selection is second to none and they usually mention where your box came from (sealed case, a return with black marker across the top of the box, unopened box etc.)
"They've done studies, you know. Sixty percent of the time it works every time." - Brian Fantana from the movie Anchorman