Generally I think items offered for commission sale fall into two camps, the first are very desirable and expensive that will sell quickly but the buyers are more likely to buy from a shop with some form of guarantee and possibly pay with a credit card, those items will make money for the shop and raise the seller the same amount as they would get privately even taking the fees into account, the other type are valuable but unusual and probably not on anyone's radar, hanging in a shop is the best place to achieve a decent sale price for those.