How to tell if a business is legitimate:
-Contact info- if you sent off money and never heard from them, is there a phone number? A physical address? Pictures of a store? A real business WANTS people to come check out their store. A scam is liable to be a couple of guys working out of an office or house, and doesn't want anyone to know there's really not a store.

Check the brands they carry, then check on some of those brand's website, and see if that company is listed as a dealer. If they say they'll sell you a Trek, and Trek doesn't list them as a dealer, that is NOT a good sign.

Do they sell bikes online that the manufacturer doesn't sell online? A lot of bike brands will sell ONLY through retail stores, not through mailorder- and if you see those brands advertised through online sales, something is funky.

Check the prices. If their merchandise is half the price of any legitimate dealer, there's probably a reason. If an operation is a scam, they can "sell" a $5,000 bike at $2,500 or at $25, it doesn't make them any difference. For a legitimate business, they all get the bikes from the same places and have similar overhead, and their prices on larger items shouldn't be drastically different- especially, drastically cheaper.

Check the stock. A real bike store will have a limited selection of sizes, brands, colors, etc. A scam store will have every bike out there in your size, your color.

Are they far off? Across the ocean? In a foreign country? That doesn't mean they're not legitimate, but if you do have any problems, your odds of having a satisfactory solution are much lower, and it is much safer for them to run a scam. If I was going to scam people out of thousands of dollars over the internet, I'd be foolish to cheat people across town- they'd come looking for me!

Is it too good to be true? If name-brand bikes were reliably available by mail-order from overseas at half the normal prices, rest assured you would read a LOT about it, and about how to get your $5,000 bike for $2,500. I've NEVER seen any indication that people were able to do this, though.

If they're not a legitimate business, what are they? There's no telling. Maybe they ARE legitimate and just do a poor job of demonstrating it. Maybe they're selling counterfeit merchandise. Maybe they're not selling anything, just collecting money.