This article is from the Toys FAQ, by firstname.lastname@example.org (Scott Gordon) with numerous contributions by others.
From the rec.arts.sf.starwars.collecting FAQ:
"Well, the best way to do this is to observe several and watch how
they are conducted and then to post on your own. Several
guidelines usually serve to help things run smoothly like:
1. Make clear the currency that you wish to receive
payment and the form in which you would like that money
(Money order, check or credit card).
2. Post accurate descriptions of the pieces you are selling.
This limits problems down the line with miscommunication based
on what was being sold.
3. If you have an idea of a price that you will not sell below
then post a minimum bid for the item in question.
4. Post or [preferably] mail frequent updates so that bidders
know where things stand."