We've all seen the tempting offers - a "free trial" which lets you sign up for products without parting with a single penny.
It can seem like the perfect answer when you're short of a bit of cash; why not enjoy the latest DVD releases, or try out that anti-virus software for free and see how you like it?
Millions of families are doing it - in fact 18.5 million people signed up for some kind of free trial this year, research by Capital One shows.
But as all parents know, when something seems too good to be true it usually is - and lots of us are getting stung when we forget to cancel the service when the introductory period has ended.
Nearly a quarter of us have paid an average of £42.50 after forgetting to cancel in time, while 11% have been landed with an average bill of £35.20 after signing up to a subscription service without even realising.
So free trials are a great way of trying something new, or getting a short-term freebie, but only if you're on the ball - make a note in your diary of when the deal ends and you can enjoy all the benefits without getting hit by an unwelcome bill.
Better still, focus on ways to cut your shopping bill without having to sign up to anything, for example via discount vouchers that will bring you instant savings.