I am bootstrapping a SaaS product with a 7 day free trial (no credit card required).

Few weeks ago someone wrote a blog post about services that have free trials and mentioned my site. Since then, I have been getting very high number of signups using fake names. Most of these users try to host phishing pages, send bulk emails, try to upgrade using stolen cards and in some cases try penn testing the service.

So far I have been successful in blocking spam emails and penn testing attempts, and stripe has been blocking stolen cards, but it's taking up significant amount of time per day.

I am considering $1 trials, but don't want to discourage legit users from signing up.

Since signups are not from any specific country or email provider, Are there any services that can screen each signup? I'm currently testing Maxmind minfraud with poor results.