I always wanted to know how do people manage to crack Reddit accounts. I had the contact of this kind of seller, but the thing is that after buying 10-20 accs from him half of them will be banned for sure. I think that he doesn't even use them for upvoting or other stuff. He just sells them to such fools like me)
People use dorks and existing combolists or straight bruteforce. It's just based on weak security of the account owner, for example weak password or they use similar passwords in various places. Once DB's get leaked and cracked, the same information will be tested on various websites.