I thought about having the bot periodically check prices of certain items you sell and change them accordingly so you always place top.
With configurable limits per item and maybe something to adjust it back to a higher price if there is no item from another player.
Since your items get withdrawn from the market everytime you call your retainer a workaround I currently use is having the retainer with the most valuable things outside of my house. You can then compare prices from there without calling her.
So the bot could just stand at your retainer, check prices and walk to the next bell to change accordingly.