What to do after getting scammed?

So it happened to me after couple thousand hours.

I was tired and lost 20div to a guy (name removed) trading a Very large -5 Controlled Meta (worth 3d) instead of Massive -5 (worth 23d).

Is there anything I can do besides move on and become better? And does GGG take action and scummy individuals like that?

You can report them to GGG.
Just move on and consider it a lesson.