I think its really important to practice good business. If there are any stores that rock, you should let them know what they are doing right, tell the managers if a sales assosciate really helped you out. I know that when a customer really appreciates my help and tells a manager, it is better than any tip I could ever get. I also think we should let businesses know what they are doing wrong, if someone is extremely rude to you or tries to rip you off. I think this is especially true for designers. Designers, if a buyer has ripped you off you should let the customers who shop there know that they are buying ripped off goods, because if they rip you off it's more than likely that they've ripped other people too. So, here are a couple websites to help you do just that!
Retailbeef.com ~ Great for designers
and my personal favorite...
Yelp.com
Here you can find almost any store and give them props or let people know your bad experiences, you can also add a store if its not in their directory and be the first to leave a review. Yay!!