Housing merchants

[LostXonx]

Are there any nods you can have on your housing plot that will act like a market board just for the items you give them?

[Greyhawk]

You can have a mannequin inside or outside, but it takes up the retainer spots (20) to sell items, and equip it with armor. So, for instance you can equip five armor items on the mannequin and have 15 slots left over to sell from, as it is based off of one retainer you have already. People can walk up to them and buy items if they are up for sale.
If you are looking for an actual MB where you can buy and sell items, no. You can with the companion app though. Two items a day if you use the free portion (you need those nuts you accumulate per day, and I believe more if you pay extra to have it.