The canonical case on the subject is Feist v. Rural, in which the Supreme Court held that copyright does not & cannot protect “facts,” essentially for somewhat inchoate constitutional reasons. As a consequence, copyright can protect a particularized expressions of factual information, but not the information itself, and if the information can only be expressed in one or a limited number of ways, it can’t even protect the expression. Feist v. Rural said that copyright couldn’t protect the white pages listings in a phone book for that reason. The one possibility would be if the Artfacts price data involved interpretation, as courts have held that the information in auto “bluebooks” could be protected, as the price estimates involved judgment. But that would still only prohibit wholesale copying & pasting & would only apply to the price estimates, not objectively factual information about the works. Which honestly, price estimates arguably are. Or at least, what if the copier considers each estimate & concludes it is correct?

The Terms of Service issue is not about copyright at all, but a contested internet law issue about whether internet service provide can & should be able to control how you use information you obtain from them by requiring you to agree to terms of service before you use their website. In other words, Artfacts could say, by buying a subscription, you agree not to share the info we provide in certain ways. Doing so could be a contract violation & potentially even criminal, under the Computer Fraud and Abuse Act. That is really not my area & my knowledge is limited, but the statute is written REALLY broadly, so who knows what they could do with it.