affiliate sale tracking

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I want to pay a commission whenever someone buys a service I am providing.

I want to track it two ways. 1. An online affiliate program so those placing links to my site through which customers arrive receive a commission. 2. An offline programs so that when purchaser's purchase and identify the friend who referred them, the friend receives the commission.

Any suggestions about what to do in a situation where a friend refers the purchaser to the web site only by name rather than url and the friend arrives online from an online affiliate link?

I guess I could have a form that asks whether there was a friend referral. Then would I pay two commissions? Would I half each commission? How would the online affiliate, or myself, be able to verify that a friend was not made up on the spot to save a few bucks? I could require offline "friends" to be registered as referral sources prior to any commissions accruing to them.

I could assign offline people affiliate numbers and require the purchasers to type in the offline affiliate numbers when joining.

I am thinking the offline program would cause problems for the third party services.

I could state on the online form that if signing up online, then there is a priority that pays the compensation to the online affiliate. I could have a separate fax or mail in form that automatically includes the online affiliate number to be used in case no offline referring friend is named on the faxed or mailed form. If no pre-registered friend is named, then I could pay to the online affiliate. This would still require the online affiliate to trust the offline process.

Any suggestions for how to do this sort of thing?