"We promote your book, and earn $4 from every book sold."
At POD prices that is probably either a pricy book or very little profit left? The site is also littered with typos and very poor grammar--never inspiring. My bet is you buy 5 or your own book, pay to send them to his 'store' and don't sell them. Where are their customers coming from? And that doesn't even touch the idea of paying a monthly 'subscription' to list with them.
Even if this service were FREE it wouldn't be worth it. This company does four things:
They make a webpage for you on their site--which, as one of scores of similar book display sites, probably gets very little traffic (you could make your own webpage, and probably drive more traffic to it yourself).
They create a press release and send it out to a few places. Press releases are among the cheapest and least effective of all promotional strategies; newspapers and magazines get a ton of them and they are as likely to be tossed as looked at. Plus, you can easily write and mail out a press release yourself.
They spam. Yes, they say that those bulk emails and faxes are targeted. But believe me, spam is how the recipients will regard them.
They give you some lists (such as a list of "national publishing companies," that you could easily compile yourself.
PSMG Bookstore is a prototypical example of the many "book marketing" services that are springing up all over the Internet, spurred by the growth of POD. Most of them are completely worthless, and some are even more overpriced than this one. Save your cash.