If a visitor clicks on ads from multiple campaigns before converting for a goal, which campaign gets credit for the conversion?
UTM will attribute the most recent campaign information to a conversion. For example, a visitor may initially reach your site through a CPC ad and not make a purchase, but does sign up for an email list. Later, this visitor may return to your site via a tagged link in an email to make their purchase. In this case, UTM will attribute the more recent campaign information to the resulting sale - the tagged link in the email.
This behavior can be modified by adding the following to the end of all of your tagged links:
&utm_nooverride=1
When UTM detects this variable, it will retain the first campaign's information, irregardless of which links the user later followed to arrive at the conversion. In the example above, the conversion would be credited to the CPC campaign, if both links were tagged with the nooveride variable.