Good point, Razor
Since this thread began, two of the sites are no longer available for our authors:
www.maidenheadbooks.com
www.bondagebookshelf.com
Now about releasing sales numbers:
Most sites have posted their payment policies in great detail. If you submit a book and are accepted, each seller/publisher will provide you current sales for biz tracking purposes. Will they provide you with information about sales of other authors? You have to ask them directly. I'd expect a no.
You might want to contact other authors privately and ask them if they are pleased with sales an specific site or with a particular publisher.