A "trial offer" is the opportunity to buy or use a product or service free or at a reduced price for a particular period of time in order to encourage customers to buy it.

Other "free" offers enroll you in clubs or subscriptions. For example, a company might offer you an introductory package of free books, CDs, magazines or movies. If you sign up, you may be agreeing to enroll in a club that will send you more products and bill you until you cancel, or to a subscription that's automatically renewed each year.

So how can you avoid the costs that might be hiding in free trials?

Here's what to do:

• Research the company online. See what other people are saying about the company's free trials — and its service. Complaints from other customers can tip you off to "catches" that might come with the trial.
• Find the terms and conditions for the offer. That includes offers online, on TV, in the newspaper, or on the radio. If you can't find them or can't understand exactly what you're agreeing to, don't sign up.
• Look for who's behind the offer. Just because you're buying something online from one company doesn't mean the offer or pop-up isn't from someone else.
• Watch out for pre-checked boxes. If you sign up for a free trial online, look for already-checked boxes. That checkmark may give the company the green light to continue the offer past the free trial or sign you up for more products — only this time you have to pay.
• Mark your calendar. Your free trial probably has a time limit. Once it passes without you telling the company to cancel your "order," you may be on the hook for more products.
• Look for info on how you can cancel future shipments or services. If you don't want them, do you have to pay? Do you have a limited time to respond?
• Read your credit and debit card statements. That way you'll know right away if you're being charged for something you didn't order.

If you see charges you didn't agree to, contact the company directly to sort out the situation. If that doesn't work, call your credit card company to dispute the charge.