Not quite: maybe I just want to put all my stuff in a truck, give it to a guy, and get a check. I don't want to worry about shipping and accepting payment from a hundred different people and keeping my listing up to date and figuring out pricing and not getting scammed.

Not at all. They are platforms/marketplaces who collect fees for bringing buyers and sellers together (or employers and job seekers).

They do not keep inventory or buy anything.

But that is the pawn business. Anything else is a different business entirely, e.g. being a second hand goods dealer.

Pawn shops can deal in second hand goods and often have the licenses for outright purchase (which may be where some of the confusion that I've seen from people originates), but that is not strictly speaking what pawning is.