I took part in a Square promotion earlier this summer by referring a friend to their service and received this email:
At first I was psyched for the $1 but the more I think about it the more I think I got the short end of the stick. If I refer ten people to Square and one becomes an active user (however they define it) then Square's cost of acquiring that user is $10. My guess is that the value of a new Square account holder is way more than $10 which means I've sold out my friends (and their email addresses) for way too little money.
To Square's credit at least they pay me something to get access to my friends and family. Better than those companies/apps/services that don't have the good graces to pay your when they "access to your contacts list" and blast everyone you've ever met with an invitation to join.