I bought a CD off of TV about 10 years ago.
About one year later I got a $180 charge on my credit card for some kind of consumer group membership, so I called em up and was like what the hell??
They said that they had my credit card number through this purchase, and they sent me something in the mail, and since I never responded, they charged me the membership fee.
After I got that taken care of I decided that I'd NEVER order anything off of TV again. They all have this fine print on the screen that says you sign up for this and authorize such and such charges unless you cancel. There's no way you can read it on the screen unless you have TiVo, pause it, and get out your hugh powered binoculars.
IMO it's always a bad idea. And I really want to get a Sham-wow too.