Cookie stuffing happens ... what can you do about it.
Affiliates Marketing is usually not seen as effective because there are bad sheep across the industry doing "Cookie stuffing".
What is Cookie Stuffing? - digiday.com/media/wtf-cookie-stuffing/
Tracking with partners your internal metrics and metrics as tracked by them is an excellent way to start monitoring variances and identify tracking issues.
Other issues, such as quality of traffic and attribution of course, need to be considered too.