Jeri, great idea about changing bits of your address legitimately to see if it improves credit. I'll have to try that if I start having problems!
I did Overnight Genius, through IPz, and it credited just fine.
To cancel, I had to call and get an RMA#, and mail back at least one of the 3 CDs. They did not ask me why I was cancelling or try to convince me to stay. Easy and cheap to return, because it was just a CD.
They didn't try to charge me after I cancelled.
I just signed up for Advantage Language, through MPC, and it credited very quickly but I haven't received the products yet so can't comment on that yet...
I'm loving MPC, btw. I'm up to 21 approved offers, totaling $144.70, have another 15 pending (about $75, if they credit), and haven't had any denied!