The biggest problems with pay for performance are trusting the client to report sales accurately, defining where the sale came from, and conversion issues beyond your control..

#1 is easy, if you don't trust them to report accurately then don't do the job even if they pay cash up front..

#2 You mentioned phone orders.. Who gets credit for those?? You, them, someone else?? What if someone went to the website and then called to order a week, or a month, later?? How do you track that??

#3 Do you have 100% total control over the website?? Are you allowed to go in and make text and layout changes whenever you want to try to improve conversions??

Ask your client if their radio, tv, print and billboard advertising allows them to pay based on performance?? What we do is "advertising".. There are too many variables outside of our control that affect the final sale and to have your pay based on that is a bad idea..

We built an entire business model around this idea 10 years ago and it failed miserably then.. We spent most of our time working for free only to have clients 'fire us' just as things were picking up.. After many lawsuits and court visits, we walked away from that business model..

On the positive side, you can make a "lot" of money this way if the site and product are incredibly successful.. But this is rare and it brings it's own issues.. We worked with a cosmetics company and they were thrilled to work with us when they were paying use $1000 / month.. But when sales really took off and they started having to write $10,000+ / month checks they decided that we weren't worth that amount of money and fired us.. (note the lawsuits mentioned above)..

If the end, like all business agreements, there are pros and cons no matter how you bill them.. The final choice is yours..

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Steve : Animal Charms Animal Jewelry | Fishing Blog
I'm smelling a whole lot of if coming off of this plan.