Speaking as a guy who reads many ads, I think I'd say it depends on what ad he's referring to. If he saw you on P411, that's quite different than BP or CL for example.

Whether you choose to see him if he's not on TER or other sites, that's up to you. I'd just say that there are a lot of guys out there who are NOT on these sites...but you can still do your screening and due diligence to be safe. When in doubt, walk away. Same advice I give to the guys.

I require one of two things....

A TER handle with a long history of reviews of credible providers or full name and employment info. Far too many clowns want to post under an alias and assume we are going to accept that as verification, so yes... I require one of two things. Personally, I think I would rather part with my TER handle vs. real info. but hey... whatever lol.

don't create any profiles and handles for a while or even get screened. I usually apologize and wish the best. At this point, you can see their different attitudes if they reply sometimes in the different tones, saying "you too," or "you should feel sorry, you lose money!" Second choice of words can definitely put that person into my personal Ignore list.

I don't go by handles since there is absolutely no way to verify a handle belongs to a certain human beings or if their shared or stolen.  They mean nothing to me as far as screening, I see no protection in having a guy's handle as far as screening.   My screening is all the same regardless of where they saw my ad.