G'day TBK,
Most have multiple addresses for their credit cards. They have some cards for their personal banking use, others for their business accounts, some with multiple businesses each with their own post office box. However, with the websites that want a credit card upfront you can register the same name and address with different credit cards, one regular at the FHC did that by using one card for their membership, another card for their spouse's membership, and a third card for their mother's membership to three different sites. All they were interested in was verifying the card worked.
Now, on a related issue, a friend got one of those pay-up-front credit cards you have to refill and they could use that to sign up for a porn site that used credit card verification for proof of age due to local law, but the pay-up-front credit card didn't work on any of the non-porn sites with the free trial period. That's got to make you wonder about them as well. BTW He did the signing up on the card as part of a research project on the Internet.
My son frequently goes to a gaming sites where you have to provide a credit card as proof of age (local law but don't know why) and the site hits him up for a buck then reverses it.
Using the name and address is a good enough check for prior free membership for a lot of websites. Heck down here Quickflix gives out free trial memberships and don't ask for a credit card, but they do ask for a name, phone number, and address and check the address for the phone number against their database, rejection if another family member has an existing account.
Lots of honest websites don't require a credit card for a free trial, but all the ones I know of that do scam you for a few months fees by making it very hard for you to quit the membership.
Ernest