They might not know what port scanning is, but can they agree to "anti-fraud measures?"

Maybe they might agree to such anti-fraud measures, but I don't think they have. I don't consider 'ignoring the terms of use buried at the bottom of the page or in small print' a legitimate form of indicated consent.

Agree with you that simply putting something in the terms of use doesn't necessarily indicate agreement. If they're only doing it to signed in users, then presumably they had the terms put in front of them at some point, but I think your objection is still fair in any case.

To what extent do they need consent to port scan, though? They're not intending to do anything malicious, and in fact (assuming you are the owner of the account that's signed in) they're doing it partly to benefit you. Is there a law against port scanning? Does it affect users in any way?

What percentage of eBay users know what an IP address is?