Who buys Pokemon cards.

Broad question... many answers. Local card shops mainly, and of course individual collectors and players. Are you trying to offload all your cards? Or are you looking get cash for high-value cards and don't care what happens to the commons? Are these NrMt collectibles? Or have they been moderately or heavily played?

I work at a local card store and I'm selling some Pokemon packs to make some money

Depends on the types of packs you have.  I'd be interested if they're Celebrations packs, but then you'd have to open product to get them.