I have been using mycomicshop for at least 10 years. My only nit pick is when I flip books I bought from them back to them some times it grades out lower. Yeah, I know, different graders see different things. But if they regrade a book as a vg, they sell it as a vg.
There are quite a few people I've dealt with there over the years that are super nice and professional. My dealings with Este Bagato in the consignment area have always been wonderful. I can't say enough nice things about her.
I'd much rather sell/trade/auction my books with them than ebay. I usually send them 4 boxes of books a month.