I get them wanting someway better than email to make sure I can't repedetedly sign up for the trail, but don't fucking auto-subscribe once the trail is over.
Having worked at a bunch of SaaS products, it's actually not that shady (at least in those cases i've seen). Free users are low value but they can cost a ton in support and commercial effort. Asking for a credit card upfront is just a simple way to filter for people who actually intend to maybe buy the product.
Sorry, no. The only reason you could possibly want my credit card information is so that you can start collecting rent if I forget to cancel, which is the goal. That is an extremely shady way to collect customersmarks.
It's a con. The goal is to collect rent from people who don't actually use the service. It's basically theft.
Just use up one of those gift cards you can use in any store and use that number for free trial signups. Then they can't charge you when the trial period expires.
I know its not the point but this kind of stuff happens so please consider privacy.com. You can set a per transaction limit, monthly limit, one time use. Etc. Please take a look as it lets you do some amazing things.