You can limit it a lot to minimize the abuse. In free entrypoint, set token and context limits to be very small. Limit to 2 prompts per IP or something every X hour. That is already a substantial limit where bypassing might not provide much benefits.
Residential proxies are too prevalent for IP address limits to work effectively.
You can use cookies to track usage history
I can delete cookies to obscure usage history
You can combine it with user PC fingerprinting
You can also just ask for a login…
You could also make the wannabe user buy a $500 retinal scanner and use biometric ID ...
Is there some public research that how often, for example, people download malware that allows this?