Auctioneers generally want good stuff and take everything to get the good stuff.
If you sell most of the valuable items first on your own you may not find an auctioneer willing to take the dregs.
Rates are negotiable and depend on how bad the auctioneer wants you stuff. More value less per cent. In my area 25% to 33% plus a ten percent buyers premium. If you give hm junk to sell and he has to move it to his place then you are paying a high end percent.
An auctioneer can either come to your place or do it at his place provided he has a place. If you live way out in the boon docks the travel will eliminate some of the audience and thus may lower price paid. A good auctioneer has a following that comes to his auction house regularly. Go to a couple of the auctions and watch. You may get a feel for one auctioneer over another.
A reputable auctioneer handles all the details, collects the money from auction attendees and gives you a check for the NET AMOUNT he pays all sales tax which he collects from participants. I have seen auctioneers try to scam by deducting things that are not legitimate and should not be deducted such as if someone pays them with a bad CC. He will have the financial stability to pay you your money almost immediately.
A reputable auctioneer may be bonded or insured in case he does not pay you. Ask to see the insurance or bond do not accept yes I am.