This is how I normally do to identify scammers, with this, you should be ok for quite some time.

First of all, I do Google search with the name of the company and the word scam. Normally, there should be no page with the company listed with the word scam next to them but if you see at least one, maybe it is a scam. No need to have several pages, only one is neccessary.

Secondly, I go on a very good website, www.fraudwatchers.org who have a lsit of all website and company listed as scam. They just saved me from sending sample to a scam company.

And thirdly, just ask people around on forums just like this one. I saw a mate who've done that.

Fourth steps is that you can verify the address they gave you and find out what's really on this. Go on www.whitepages.com and enter the address they gave you to find out if the address is really registered as their business address or at least at their names

Fifth test is to ask them to phone you. Normally scammers won't do this but beware, some also tries to call you. Please be aware that some scammers uses call redirection which is call callback (I'm not sure of that) or they can use fax to email. Using this, they get number that are listed in U.S.A., U.K. or any European country where in reality, they are located elsewhere.

Sixth, alway inquire about the mail address. This is a mistake scammers often made. Try to see whether the email address comes from a free mail server. Suppose you get a mail from economicdevelopment@mail2cameroon.cc, be sure this is a scam. The mail address (it truely exist and they tried to scam me) is not from the Cameroon government, but from a free mail server. This is how I caught my first scammer.

Seventh and last advice for the time being; JUST COME AND ASK ME. Yes, you can come and ask me and I'll help you. I've been for so much time victim of scammer, who fortunately failed in their attempts, that I've got some pretty much experience.