Is this an "unadvertised" arrangement? Why not take a commission?
I used to do it as a service, and I found that it almost
NEVER resulted in a sale. Why? Because the high bidder may well have been prepared to pay much more themselves, and they may well have no interest in re-selling it. I made at least 100 offers, and maybe two or three ended in sales.
So now I solely do it on multi-hundred dollar items or higher, and the offer MUST be at least 50% higher, and there are STILL next-to-no sales. When there are, it is mostly when the person offers two or three times the selling price.
Why take a commission on something that almost never happens?
On the other hand, auctions that own a lot of what they auction absolutely
SHOULD offer this service, because they can quickly "flip" items from their inventory.