One of the very important parts in eBook selling is the Sales Thread.
You need to develop very strong relations with your buyers, you never know
, someone may buy a copy for resell rights [has happened to me twice].
Also, the other important part is promoting your thread.
You need to post around 40-50 posts/day in the section where you are selling.If you have a little money, buy some signature links for promotion.
I am sure you may have many of your friends for giving reviews, but your customers should not be disappointed after buying your ebook.
Also make a list, and give them a freebie once in a while!!

It never hurts but helps
PS:
According to me, $500 / ebook is not achievable unless you have a *REAL GREAT* method or some other stuff which you are sliing for $ 37 or something.