Should clients get refund if they forget to end trial?

I would ask yourself this, why are you making people sign up for a free trial with a credit card? Is it because you're actively looking to capture people who are forgetful, or some other reason.

Having been in sales and marketing, I can tell you that the first reason is usually why companies want the credit card information for. If the product was so fantastic that the trial will sell it, there's no reason to capture payment information during a free trial. For people who forget to sign up, when it gets automatically cancelled at the end of the trial, they'll beg to give you money. Requiring it up front is about producing a false conversion rate.

I refuse to sign up for free things that require a payment method registered. It's not free if you say, let me hold your wallet while you try it out.

Absolutely fair to ask. It would be shocking if they don't provide one, to the point that I wouldn't trust that company with anything in the future and would likely file a chargeback to get the refund.

The fact that there are now dozens of services that exist to provide you with a burner CC number in order to sign up for these trials indicate that almost nobody actually wants to provide a credit card number for a trial. It's also just ridiculously user-hostile with very little proof that it results in higher customer activation compared to a trial that doesn't require a credit card.

Good luck!

A required credit card to access a "free trial" of a product is a very widely used dark pattern.

It is always fair to ask for a refund in such situations.

If you really want to be fair you can send "your free trial ends in X days, cancel or continue" emails.