These fees are legal, they're sneaky, and they are a way for companies to make big bucks. A recent study found 35 percent of cardholders are hit with them. So went to the experts to find out how to spot and stop them.
Travel blogger Kim Orlando writes and tweets about her many adventures so she paid a company for a trial subscription to track reaction to her tweets.
"I thought I was going to pay $149 for that one month," Orlando said.
But instead, she was billed four months in a row, something Orlando says she never signed up for. Experts say a trial-subscription-turned-permanent is just one type of gray charge.
"Gray charges are unwanted, sneaky little charges that are starting to show up on consumers' credit statements and bank statements," financial expert Jeffrey Cutter said.
How do businesses get away with it? This survey found eight out of 10 people merely skim their credit card and bank statements.
"I'm embarrassed to say that it took me four months to figure out I had been billed every month," Orlando said.
What other gray charges could pop up on your bills?
Unknown subscriptions: That's when you make an online purchase and forget to click or unclick one little box, so you end up opting in for another purchase.
"Over the past half a year, we have seen more and more of these charges," Cutter said.
And then there are the zombie subscriptions. Say you cancel a gym membership or a magazine subscription, then a few months later the charges come back.
Another gray charge is cost creep, where a monthly subscription slowly increases in price.
Keep in mind, many gray charges are legal if businesses spell them out in those terms and conditions most of us just gloss over.
"Make sure when you are purchasing anything, or that you read everything and understand exactly what you're doing; that's partially your job," said Jerry Cerasale with Direct Marketing Association.
Orlando challenged her gray charges, but says the company insists she signed up, so it's now in dispute with her credit card company.
Despite her busy schedule, she's now going to check every charge on her statements and has a message for sneaky companies.
"That's just going to make me an unhappy customer. I'm certainly not going to sign up for anything that they have to offer in the future," Orlando said.
The Direct Marketing Association and Federal Trade Commission have taken action against companies charging consumers without properly disclosing the conditions of an offer. If you feel you've been unfairly charged, report it.