Question about email traffic...

Some email submit cpa offers allow for email traffic but I haven't seen any that allow you to incentivize the person to complete the offer. How does the cpa network know if you're incentivizing the person to complete it? If I say to the person I'm emailing "Hey fill out this survey and email me back and I'll give you a candy bar" how would the cpa network have any knowledge of that?

Because incent offers 9 times out of 10 are extremely low quality traffic.
With email submit's the money is made on the co-reg path. The conversion happens after the 2nd page. If it's incent, 80-90%+ will not go through the co-reg path and the referrer may be leaked and they can see where the traffic came from. The extremely low quality of traffic most of the time means incent traffic.