Here’s why affiliates should think hard before joining the Groupon affiliate program:

• There’s an e-mail wall before they see a deal and you aren’t paid for this.  Groupon is firstly in the business of acquiring e-mails and renting them out to businesses.  This means they are getting e-mail addresses from you for free.
• They pay 10% for any user that hasn’t purchased from Groupon before.  If you send them again, they pay 2%.  So they extort the local business by making them offer their products/services for 25% on the dollar (pocketing 50% commission) and give you 2%.  
• If the user clicks out from your site to Groupon for the first time but Groupon has seen them before anyhow, you get 2% as well.  How exciting.

My guess as to why Groupon is running after naive affiliates is because their SEM marketing campaigns are burning out and they must look under other far and wide rocks.

Groupon claims that their services are more than just offering a great deal - that they are publishing amazing prose in the form of product descriptions.  But let’s not kid ourselves: what is happening is they are injuring local businesses one day at a time and now extorting publishers too.