how to check if a site is safe

[#1]

I have just come across the trialpay.com site with its offer of buy one get one free, as i apply the rule " if it looks too good to be true, it usually is". has any one taken up the offer and what was the result?

[#2]

http://venturebeat.com/2008/02/20/trialpay-gets-you-stuff-for-free-with-a-catch/
http://www.pcworld.com/article/140029/trialpayfree_stuff_with_some_strings.html
Basic thing is that there is no such thing as a free lunch - if you don't really want the free item you can probably get the bought item cheaper elsewhere