Is it illegal to pay someone, non real estae feild, 25 dollars if they refer my business

Not in my opinion, but most here will likely disagree. Its the business model of Thumbtack and HomeAdvisor though.

I see some NACHI inspectors offering money to their former clients for referrals all the time.

I offer a $50 gift card to clients for 5 successful referrals ( I have to book and perform the inspection), so far only one client is close.

thank you