Not sure about the first paragraph, but the rest I agree with. Trades don't really concern GOG very much. But this is about users helping other users not to get tricked.
I thought the original question about rep pertained to the Steamgift GOG gifting club (which doesn't exist). That should be left up to Ubivis and maybe the other administrators.
For other contests and giveaways, that should be left up to the creator of the contest or giveaway. How can there be a question about that?
For random gifting, as mentioned by pH7 and possibly others, that's a random or not-so-random act of generosity. You can't really scam someone doing that... well, maybe if you're laying on some thick sob story hoping to get pity or something... that's a different story.
Same with posting codes for ninjas. You're basically throwing something out in the wild. Respect and common courtesy would hopefully cause the redeemer to at least say thanks, but sadly this is not always the case.
I think the original point behind this thread is sound even though Anasto / Wakalo / Jota / Joao changes his name on here constantly. At least it might increase awareness and if we can nail down the unique Steam ID numbers that he uses, that would also be helpful.
This thread began as a list of user IDs for a person who said they would trade and then scammed the person out of a game by breaking their end of the bargain.