I "test" sponsors all the time, as do others in my circle. I would encourage it.
A few things I'd suggest, however. First off (this should be obvious), don't defraud them. If you do some free signups, let them know once you've done your analysis.
Second, never do a chargeback. If you sign up for a month, pay for it and cancel before it renews (hey, testing costs money in this business, get used to it). For those sponsors that allow for it, let them know it was you and they will reverse the charges (many do).
If you do find fraud, however, all bets are off. If hashing it out with them doesn't pan out post it here.
Lastly...Rosalia, email me (not ICQ...I'm a busy boy these days). I'm ready to drop your program in where we talked about.
