The question has been asked before about various other retailers.

The bike manufacturers don't just give bikes away in one market or another. If someone's got 'em for sale really cheap, it's probably a scam.

A number of manufacturers don't allow mail-order sales of their bikes, period, so if you see those brands being sold via internet, you know it's a scam.

Another big tell-tale sign: If that retailer "sells" Brand X, and you go to the Brand X website, look up authorized dealers for that area, and they don't list that retailer, it's a pretty good sign a scam of some sort is going on.

If they sell EVERY bicycle out there, that's not really a good sign. Real retailers are limited by warehouse space and agreements with manufacturers as to what they stock and what they sell. A scammer can list every model of bike in the universe on their website, doesn't cost them anything.

It can sometimes be illuminating to look up the contact info for a retailer. Most legitimate businesses will have a street address, a mailing address, a phone number, a fax number, etc.- they WANT you to contact them any way you can manage. If the only contact is via the internet or email, thats a bad sign.

Consider also the complications that arise if you have problems with a retailer. You can't just run down to the small-claims court to take care of it- you're pretty well stuck if you have a problem.