I've bought and sold a few items in the EE in the last 6 months, and I have had a few great experiences and a couple disappointing ones. Here are a couple recommendations:
1) If pictures are available, you are required to post them. Anybody that has the ability to email pictures has the ability to post them using Imageshack or some other free service. A lot of the negative feedback/misunderstandings on this board could be avoided with detailed pictures. There is no excuse for saying "pics on request", because for a high demand item buyers are unwilling to wait on pics before saying "I'll take it".
2) You are required to give an NRA rating to all equipment: New, Like New, Excellent, Very Good, Good, Fair, Poor
3) You are required to give, if known, the maker of any equipment (DPMS, Colt, RRA, etc)
4) You are required to make a statement as to the functionality of the piece of equipment (jams, eats batteries, won't hold zero, unknown, etc)
5) All payment and shipping arrangements will be made via email (NOT IM!). Shippers are required to email the buyer on the day the item ships.