Some advice on whether I should send the giveaway key/can request a new winner? (ANSWERED)

Strong clues but no evidence, I'm afraid there is no ground for reroll. You could report him to bring him to support attention, but they don't even have time to deal with real, proven rule breakers, so I'm afraid they won't have time to investigate this one.

You could just send him the game - I know, it hurts - and then blacklist him if you think there are enough elements to support your suspicion.

edit : have you checked for unactivated wins or games won twice ?

The enhanced steam browser extension will add relevant links including SteamGifts, SteamTrades, SteamRep etc. to the side of profiles when viewed in the browser with the extension installed. So grab it for your browser and check for SG profiles and such if you want and then feel free to report them if you believe it to be breaking the rules.

If you request a reroll saying you think it's an alt account, support will check.

Check if that high-level account is registered here. That is a bannable offence, so it could interest support.

only 2 friends

i know ppl here (not bots) with only 1-2 friends, its ok

What talgaby said, multiple accounts is not allowed

what they said.. as convinced as you are it can't hurt to submit a ticket for re-roll and have support investigate into it.
personally i don't' dig that deep into users, but there isn't anything wrong in doing so.

Nothing to add that hasn't already been said but have a bump anyway

Bump & thanks for the gib

Question already answered, so just have a bumping thanks!

Just bumping since you got the only solution ;)