Positive Feedback by a guy called VenganzaDulce.

This is not SteamTrades.

You'll have to keep that feedback - as you can't protest positive feedback (At least to my knowledge)

In future, the discussions here are not for discussing SteamTrades - it is a seperate site with no moderation team. What happens in SteamTrades stays in SteamTrades.

Why would you report him? I don't get it. It's not like he did anything bad.

Why would you report him for giving you stuff and posting positive feedback?

They see me trolling...

This site has absolutely no relationship to SteamTrades [At least, more recently; Earlier on it had the very light association of being linked to this site, but that association didn't mean much given that it didn't share any staff or functions with this site]. SteamTrades has absolutely no moderation staff, it's fully user-managed. It is thereby often considered significantly inferior to its main competitor, Barter.vg [which offers more features, protections, and actual moderation].

Further, here on SG calling out specific users, for any user who can be associated with SteamGifts (even just potentially), is a violation of site rules and can potentially lead to a suspension. As the name isn't important for this matter, you can simply edit it out of your thread. Meanwhile, for situations where it is important [and also directly related to SG], you can just contact staff directly through support tickets.

Should I report this to modders? How?

In short, no. And you can't. Since no trade occurred, the responsible thing would be to not reciprocate feedback and, given that the feedback they left you was positive, to just put the matter out of mind. And yes, trading can get weird at times. Not much to do about it. If you avoid clicking any links traders may send you, always only add users by directly using the profile links on the trading site you're using, and don't accept random invites, you can at least avoid any risks to your account. Weirdness of interactions, that's a bit harder to avoid. :P

Do not click on any links he may have given you. People that do "weird stuff" are often doing it because they are trying to get you to click on links. Those links are almost always malware (e.g. key loggers).

It is also possible that the account you mention was hijacked by the person contacting you. Just be careful.

VenganzaDulce means Sweet Revenge, so, there's that.