If you sell through an auction house you’ll have to wear the cost of getting the art to them in good safe condition. That itself is not necessarily cheap - if its fragile framed art it will need a courier. Depending on the way they do things they’ll take a % or pro rata commission from the final sale price. If it doesn’t sell then there are usually standard arrangements for how they deal with it - it will probably show up a few times in later auctions, maybe with a return at your cost provision if they can’t move it.
Every auction house will have a general terms of sale contract that you will need to sign before they do anything. It will be on their website or they will be happy to send it to you. Signing it is the starting point for them having an interest - but, unless you’re selling a good Picasso, they will not waste time wanting to vary those standard terms. In that sense its their show and they will call the shots. And at the auction you get what you get - its in their interest to find people interested in buying, provide trust about the identification of the item and security of the transaction.
Will you get more if you sell it yourself? With lots of the artist’s work around, do you know a way to reach the presumably very small pool of people on Earth who might be interested in yet another example of his work? If you reach just one, then will you pay what they offer? What if they offer you $500 - take it or leave it? You need at least two competing buyers to move the price above what any one might want to pay - its a buyer’s market. Can you even find two people with a lazy $7K in their pockets, both interested at the same time?
The other things that affects what people will want to pay is risk. I buy from auction houses because there is some comeback if something is not as described, but I don’t know you on EBay or a sale ad. You could be any sort of scam artist, and I will factor that risk into my opinion, and eventual offer of $100.
Also, be wary of confusing price you can achieve with the price tag someone else has on a similar piece. Q. Why is it on sale? A. Because no one’s buying that one at that price, so why should they buy yours? Gallery price will have their overhead and commission on what you get - that’s whatever. Half the sale price?
Final option - don’t sell it but make it a family heirloom. Most of its worth will be in sentiment, esp. if its a piece of genre art [what it sounds like]. That stuff does not hold its value longer term, so you won’t make your grandkids rich, but it may retain family memory.
My pick - auction house with a specialty in art. Spend money to minimise your risk - courier, conservation treatment or professional cleaning. Think of a realistic number then halve it.