Hello and welcome to the forum.
Some thoughts:
1) Some hosts use fraud prevention services (MaxMind, et. al.)
I don’t have any experience with it, but I suspect there is an easy way to plug it into the common signup portals.
2) Personally, I won’t consider using any service that requires identity verification beyond my email or telephone numbers. Services that want me to send in a scan/picture of my ID/credit card are ignored — so beware that you may be alienating some of your potential client base.
3) Even with identity verified clients, their services can still be compromised by criminals and used to violate your TOS.
4) If you’re having severe problems with SPAM, you may want to block outbound e/SMTP ports for untrusted users/require a deposit (to cover potential abuse) to unblock. Once trust is established, you can refund the deposit.
Good luck!