Short answer: any free trial that required a card will charge you automatically once it ends, unless you cancel first. That's the deal, even when it isn't made obvious.
Before entering your card for any free trial, ask three questions: how much does it cost after the trial, exactly when does it end, and how many steps does it take to cancel. If you can't find clear answers to all three, don't sign up. Services that make cancellation deliberately hard are relying on you forgetting, not on you loving the product.
A single unnoticed $10 charge a month adds up to $120 a year, and scammers count on amounts small enough that you won't bother checking.
Many banks offer virtual card numbers built for exactly this. Use one, with a low spending limit, for any free trial. When the trial ends, delete the virtual card and no charge can go through at all, no matter what the fine print says.
Check your bank statement once a month for small charges you don't recognize, especially in the $5 to $20 range. Search your email inbox for the words "subscription" and "trial" too, most services send a confirmation email when you sign up, and that search often surfaces services you'd genuinely forgotten you were still paying for.
This is one trick out of dozens. The Scam-Proof Playbook covers online shopping scams, QR codes, phishing, and more, in plain language, with real examples.