HOW CAN WE TRUST A SITE

The person who deals with any site for purchasing and selling thru a particular site, has one particular problem, how can he trust a person or a company which he cannot see and many times he is from a different country?
I use a particular test for this. I try to find out from ip location location , from which country he is . Secondly I try to find out which payment processor he is using. I usually deal with persons who have a pay pal account and more if the pay pal account is verified. If the stranger is using an un-heard payment processor , you should best avoid dealing anything with them.
You can also test the stranger by purchasing the first minimum lot,