bigjohnt - 3:34 pm on Oct 6, 2006 (gmt 0)

Keep monitoring your referrals after an agreement. With a PPC vendor that gave me an agreement to only send US traffic, I was receiving THOUSANDS of clicks from Paraguay, Uraguay, Argentina and beyond. I found the spikes by looking at hourly traffic, and seeing major spikes at 2 and 3 in the AM (EST) not a period when a lot of US users are online.

They would tap out my account in two days. This was apparently not seen by the vendor, because they "used third level partners and could not be responsible for traffic from outside their network."
After 4 seperate instances of the SAME PATTERN, and reimbusement in the form of (worthless)credits to the account, I dropped the vendor. Even showing them the logs of fraud from their partners, they would not drop the partners. Apparently few large businesses check their referrals, and they just continue to pay for bad traffic.
This was in a very highly competitive category, subject to clickfraud all over the place.
You absolutely have to keep checking your referrals. I use a third party tracking system.

Trust but verify. Then verify. And verify again.