wtf with the fake -rep

You can try to add him and see what he has to say (hint: make screenshots of your chat).

A scammer is probably involved here. Nothing you can really do but talk to him and hope for the best.

Don't worry. You're not the only one who's dealing with that. And I doubt that reporting/making a ticket will help. Mine has been on for months and it's still pending.

don't worry about those negative reps, anyone with some common sense would check the person commenting and see he/she has been around for ~5 hours without even a steam profile.