I usually base on a few things.. and this is just me..

 I tend to look closely at the product.. I examine each and every promo with a fine tooth comb..LOL Then I read reviews.. I fi like teh promos and it has quite a few good review I look to see how many "over the top" reviews it has.. you now the ones just gushing with THIS IS THE MOST FANTASTIC INCREDIBLE LIFE ALTERING PRODUCT EVER!!!!!! 3000 STARS!!.. those types.. if it has a lot of those I look at the merchants other products.. are there product reviews like that for their other products?  More importantly.. are they from the same reviewer(s) that gave the other gushing reviews.. if they are I tend to think like you.. that they may just be friends of said merchant trying to promote sales.

Renderosity's "problem Child"
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