Keep in mind that any auction house gets a percentage of the sale from the seller in addition to the buyer.
On occasion, if you have a very expensive, high grade collection the auction house MAY waive that percentage of the buyer.
For the average seller, if you have the time or patience, selling it yourself is a better option.
You can sell it fast, through an auction and not get what they are really worth at the end or sell them slow yourself and maybe get what they are worth.
The above is based to selling my father's guns when he passed. He had decent guns, well taken care of, but if I had the time, patience and motivation, I probably could have gotten another $5 k - $10 k based on what he had.