[kulor]

I don't suppose it's a problem that can be fully solved; just an ongoing arms race. The hardest part is not deterring genuine users at such a decisive consideration stage.

[cranberryturkey]

That's why I don't want to add a captcha.

[Meganet]

Just accept it if they don't verify it anyway.

Make sure to have good KPIs not using the pure number of accounts. I think its absolutly valid to have it like that.

IF you really don't want to use a captcha, why not write something very basic specific to your page?

Those are probably spam bots filling out a basic form.

[gnz11]

If you are OK with running a Google service, how about Recaptcha V3? No captcha to fill in, just validate the score it generates on the backend.