A mall project already failed.
It was determined that the failure came from the facts that humans need sleep, and therefore most people can't be there 24/7, and can't maintain a virtual business at that pace (all their online time) for more than a few weeks.
Eventually, people want to do something else than waiting on people to buy/sell stuff.
A mall has so many disadvantages, yet no real advantage, except maybe on price.
Then again, did you really save caps if you could have saved litterally minutes using a simple command?
No chat, no bartering, no trouble.
Don't get me wrong, I love the black market. Yet I don't feel there needs to be a centralized location for the black market trade to take place. Bartering via private message is way better, and allows me to barter while doing something else, then if the deals falls short, I didn't tp for nothing.
I just need to state in chat that I'm buying gunpowder, and everytime, I get a few /msg from people willing to sell.
Dynamic shop, as Bird said, wouldn't sustainably last long, and eventually make everyone angry.