My friend’s a dealer that does stuff like this. Basically her and a friend will go through the house, pricing everything. My friend either knows the price of something offhand, can look it up, or, worse case, will consult with another dealer specializing in that item. It can be tedious and time consuming.
Then they’ll offer the merchandise to other dealers that can come in and scoop up a bunch of merchandise, or my friend will buy it herself to re-sell. If something is really valuable, it might get sent to an auction house.
After that’s done, it’s time for a yard sale, the remnants of which go to a thriftstore or a landfill.
I don’t know what percentages are but don´t just go with the lowest bidder. The ability of people to absolutely fuck you over here is EXTREMELY high, so you want to have people with sterling reputations over people who are low-balling you.
Go to antique / thrift stores / consignment shops in your area and ask around for dealers who can do this.