When I sell something in the Market,
how does that differ from “Craigslist”, (after all craigslist is free)?

    

With the Alpha Mall, your item ad includes your Paypal button, so there are no bothersome phone calls. 
There is also no need to cancel your ad when you sell your product.  Once an item is purchased, it disappears from the Market.
You receive notification via e-mail when your product is sold, ... then just ship it out.