Most of us put a lot of trust in the banks we use. We trust them with our money and, I dare say, we trust them more than other businesses to look out for our best interests. Sure, they need to make a profit, but they’d never do anything that wasn’t totally legit. Or would they?

Banks are now sharing their customer lists — and account information — with third-party marketers. And from what I can tell, they’re not always picky about who they partner with.

The surprise check in the mail

“A $10 check is a nice surprise,” the letter from Travelers Advantage says. “Especially since it’s yours for just reviewing the benefits and privileges of this national savings network. And there could be more checks coming your way!”

If you read all the way to the end, you’ll see that “Your credit card account on file with Travelers Advantage will be automatically charged for the membership fee when you accept this offer unless you cancel during the thirty-day review period.” But the letter doesn’t say the company is teamed-up with your bank and has a way to bill you, even though you aren’t asked for any account information when you endorse the check.

Travelers Advantage is just one of several dozen names used by the Trilegiant Corporation of Norwalk, Conn., when sending these $2.50 to $10 marketing checks. The Better Business Bureau says other names include: AutoVantage, Complete Home, Shoppers Advantage, Buyers Advantage, Pet Privileges, and Just for Me.

California sues

Last year, California Attorney General Bill Lockyer filed a lawsuit against Trilegiant and Chase Bank, alleging they worked together to create and carry out a marketing scheme that, he says, “unlawfully deceived tens of thousands of California consumers” into paying for these membership programs.

“After tricking victims into joining,” Lockyer said in a news release at the time, Chase and Trilegiant “used deceptive billing practices to maintain their ill-gotten income stream.”

California’s lawsuit, which is still pending, says Chase customers did not know that by cashing that check and accepting the “free” trial offer, Chase allowed Trilegiant to charge their Chase bank accounts or, in some cases, add fees to their monthly mortgage payment.

Other banks also teaming up with Trilegiant

Mark Capano of Troy, N.Y., recently received a check from Trilegiant for $8. It was sent to him as a “valued Household Bank card member.” By cashing the check, he would be able to try a buying club called CompleteHome Savings “risk free” for the first 30 days.

The huge block of copy above the endorsement line on the back of the check stated that if this trial membership was not cancelled in time, he would be charged $99 for the rest of the year and be automatically renewed for a second year at $109.99.

Capano, who is a bit hard on himself, told me he was “a complete idiot” for depositing the check. But he figured since he never gave the company his credit card number, there was no account for them to charge. Capano didn’t realize that since Trilegiant was working with Household Bank, they already had his credit card number.

“It’s extremely misleading,” he says. After complaining, Capano was able to get a refund of $66. He’s still out $33 for a service he never used.