What is your anti-fraud/anti-abuse system?
I plan to add multiple checks on registration to ensure that registered users are in fact potential clients and not fake emails or potential abusers.
My plan right now is to use Clearbit Risk https://clearbit.com/risk to block completely everyone over risk score of 85.
And on top of that everyone that is able to register will have to verify their email before accessing the dashboard. Non verified users will be purged from the DB weekly.
Next they are free to use to system but without actually deploying anything until they enter their billing information.
I was wondering what measures everyone else takes against spammers, hackers, abusing users.
I worked in the insurance industry on automating fraud/compliance and anti-money laundering. There are free, text-file, lists from most major governments around known terrorist suspects and money launderers. Not sure how big you're thinking but that's certainly an option.
I would also suggest:
1.) IP geolocation with a risk score for high risk locations.
2.) Blacklist or at least assign a risk score for certain email domains. I like the score idea here because mail[.]ru can generate a high score, while free emails like Gmail can be a moderate score, while personal/company emails can be a lower score.
3.) Identify behaviours or sequences of behaviour that are potentially malicious, log those, and assign a risk score to those to perform those. For example, I think Twitter shuts down accounts that create a new account and immediately start @ tagging other users. For you it might be if they sign up, don't take time to explore the product, and immediately perform high-risk behaviours.
Hope that helps,