I do a lot of trawling around local and small scale online auctions for coins - both bulk lots and individually. You get to spot the different sorts of bulk lots after a while - there are some that are genuine "Grannies old jewellery box" lots, and that is what you really want to find. There are some lots that have had a cursory, non expert, sort - these generally have any gold or silver removed or put into separate lots, but may still have a few interesting bits left. (The non-expert rarely looks closely at coppers or tokens and has poor knowledge on foreign pieces, so you can do well there.) Then there are the dealers' junk lots - accumulations of the coins they cannot sell, sometimes salted with a few slightly better things to tempt the bidding and persuade you they haven't been through it with a fine tooth comb.
Telling the difference is not always easy as some dealers go to great lengths to make the lots look original!
But they can be great fun and provided you know your stuff and view carefully before bidding, you can do very well.