What would I do if someone scammed me on here?

There's some, but not common.
Also "scammers" probably is not the correct term since you lose nothing (besides of your points, but well, they are regenerating).

Haven't had a single one yet.

Fake giveaways make up a small percentage of the total on here, and usually result in confusion about how the site works, or plain trolling (which, thankfully, is fairly rare). From memory, over 95% of giveaways are successfully delivered.

Trolls don't last long and, since the site requires a Steam account with $100 of games activated, they rarely return. The mods are pretty good at kicking douchebags into touch, and it doesn't take long for the law to catch up with miscreants.

Most fake giveaways are for high value games, made by new gifters. That's not to say that ALL such giveaways are fake, but these are in the "high risk" category. If you want to enter, nobody is stopping you, but you should be aware of the lower chance of receiving the game, should you win.

I don't think it's correct to call such "gifters" scammers, as most simply don't understand how the site works. Whether it's expecting to receive the game rather than actually having to provide it for the winner, attempting to gift non-Steam keys, or some other ill-conceived scenario, the "gifter" never actually receives anything from you, and ends up with their reputation damaged through negative feedback (ie gifts marked as "not received"). All you lose is your points, and that warm glow that initially accompanies the joyous appearance of the green bar...

Just be aware of what giveaways you enter, and the gifter's track record, and you'll be fine.