To know that site legit or not you can follow these methods given below:
You can read user reviews, problems, their quires, responses and rating about the site in http://webutation.net   

You can also do a whois search in the site WhoisXY.com  and know the owner, technical, administrative contact details etc.. you can use the phone number or email id which you get in whois search and try to contact the person and clarify your doubts.

If the site has SSL certificate it is good site for transactions. SSL certificate enabled site looks like https://paypal.com.