Easy start off solutions are ETSY.com and Shopify.com. Will be doing some more research into this.

I've had some experience with Market. 
http://www.markettheme.com 

It's a theme that adds shopping cart capability to Wordpress.  Your customer then submit payment through Paypal.  It's easy to use, and comes with a product manager plugin that helps you manage your product entry & editing through the WP administration area.