I signed up for a 2 week 'free trial' for Stamps.com when I was trying out that ******.com thing.
Within 24 hours I had both sent them an email to cancel, and submitted a cancellation thru their phone support.
That certainly didn't stop them from billing me repeatedly, causing the Paypal account card that I had used to go into the negative, shutting down said Paypal account, and causing nothing but headaches. To this day they are STILL trying to get money out of me via collection agencies. I haven't seen tactics like that since I worked for CCBill. They continue to claim that I never cancelled the account within the trial period.
So.. if someone wants to try these guys out, at least use a single-use CC number (if you have that option.)