One of them did not validate the card number, so you could just type in 000000000000 or whatever and your free trial was enabled for a month or whatever and then be auto cancelled when they tried to bill for your first month after the trial. In the UK though local calls were not free and charged by the minute.
I think that ISP also bundled a Good times.
Edit: I think the version of netscape/Mozilla was this one - I distinctly remember the "M" logo that would rotate as pages loaded slowly on a 14.4 modem: https://www.webdesignmuseum.org/uploaded/old-software/web-br....
Curious that it was called "mosaic netscape" - I don't remember that.