Used in a sentence, the term would be "The salesman said they were selling the item on ..... so he'd need to ask the owner if they could accept my offer of $200."
Suppose you want to sell a piece of art (or any object, but it was more common with art), but you don't have the time and storefront to personally sell it, and don't want to auction it. So, you lend that artwork to a store owner so that they can try to sell it for you. You'll tell them the minimum price you'll accept, and arrange for the salesman to receive some percentage of the sale price or a larger portion of whatever amount they can sell it for above your minimum price. If the item doesn't sell (usually after a month or so), the store owner returns the item to you, and no money has changed hands at all. Throughout the process the original owner will retain legal ownership, until (and if) the salesman can find a customer. If a customer is found, the salesman handles the sale, and gives the creator their portion of the money from the sale.
There is a specific 1- or 2-word term for this kind of arrangement, but I can't remember it for the life of me. Google has not helped me find this term, probably because companies like Amazon use the reverse of this sales model. And the next best set of search terms just returns results for pawn shops (as those businesses both lend and sell, but that's completely different). The overall process is a bit similar to the occasions where an art collector lends famous pieces to a museum for a year.
Edit: thank you to the comments and answers, "consignment" is the word I was looking for.