You've probably had an experience like this: You're completing a purchase at an online shopping site when an offer of free shipping or cash back pops up. You accept the offer, and a couple of months later you notice that your credit card is being billed $10 or $20 a month for membership in a travel or discount shopping club. You didn't realize it at the time, but by accepting that tempting offer, you joined the shopping club and agreed to pay the monthly dues it charges.
The companies behind these clubs, called posttransaction marketers, have been under fire recently from consumers and politicians who claim that their offers are deceptive or misleading. Here's a look at how these companies sign up new members.