Question
I use UTM parameters to track all the links I use on different advertising channels (Adwords, FB ads, Bing ads, etc.).
However, since UTM parameters will cache when a user first comes to my website if that user initially came from a Facebook Ad, then left my site and came back through a Google Adwords Ad the UTM parameter will list Facebook Ad but the conversion actually happened with the Adwords ad.
So my question is how can I track if Facebook ads is actually helping/complementing my Adwords ads?
Answer
Facebook's built-in conversion tracking does a really good job of sorting these things out. They run some complicated scripts to determine whether their ads was the origination of a conversion.
However, if you really want to do your own segmenting I'd work out a system to send users to a unique conversion page based on where they entered the site. It's actually pretty easy and and would give you a definite answer as to where your best / lowest-cost conversions come from.