Legal to refer yourself?

I have not tried to do this myself yet, but I have thought about it several times. In many programs you can sign up as an affiliate without being a customer or a member. You can earn money by referring other people to it, without using it yourself. What if you sign up as an affiliate first, then become a member from your own affiliate link. You would then earn a commission from yourself every month. As I said, I have not done it myself and I am not sure if this is a legit way to do business. For instance, you can sign up as an affiliate of Aweber (a great autoresponder by the way) and become a member from your own affiliate link paying the $19.95 a month, you would then get it cheaper because you would earn a commission from it every month as well. What I am asking is this? Is there a general rule / law against this, or do every company have their own set of rules regarding this? Might it be legal / legit at Aweber and not at Getresponse (another great autoresponder by the way)?