Is what this site is doing with steam community legal? https://www.steamtrades.com/
I assume that is a grey area, no? So what are the factors that would make it legal or not? I assume one should not show too much content from a user's post in the preview, not sure about the avatar and user name/reputation (GDPR). About the search itself - I am not sure whether it is allowed to aggregate one user's posts; might also fall into GDPR, no?
And what consequences can you expect? With GDPR violations (worst case) I assume a 5 digit fine would be possible? Then what about the rights of the original website? I assume the common practice is to send a cease and desist, but not to sue for damages in the first step?