Its not very accurate to sell stuff by using the normal market in both cities. because players have to get into the seller's house to by stuff. I donno about black market.
Thats why I tried to tell ppls yell for sell/buy in "market" channel. you can do the annocement in the channel so everyone can hear your auction wherever they are as long as they joined the channel.
try spread this in your server. its a pretty good idea and you can sell/buy stuff faster.
There's no need to set up Visitor as a default. When you begin selling your items your home changes to Visitor if its not already. When you stop selling your items it goes back to your settings.