Here is some info I use to prevent me from getting scammed from websites selling AS:

I have a good tip for people who want to use a .com site. Most of these sites sell a particular UG lab that has their own website.

1) Go to their website (the UG website)
2) Type in the .com website in question (there is a link to this on the left side of the home page)
3) The UG lab website will tell you if that .com website is a direct buyer.
This is not fool proof, but is a good indication that the website in question is doing good business. I have used this method and have 100% success rate, and no scams.
The only problem is that the .coms are usually pricey.