We use a honeypot. There is a field on the registration page that is hidden using CSS tricks. If it is filled in when registering, the registration is ignored because no human would ever have even seen it.
Captcha’s don’t work. People are paid (tiny amounts) to break them.
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The problem with reporting these, is that this spamming can be done as a tactic to defame a competitor. Therefore the appears the competitor is web spamming. If it were as simple as banning all domain names used in spamming, everyone would have done that long ago.