Was I kidding when I bought it?

I bought a second hand samsung i3 laptop on facebook for 150 euro now i checked youtube what it can do and the one in the videos looks completely different from the one i have, is that a fake laptop?

Yes.

What can i do now against the seller? He'll certainly deny it

I3 is a processor series from Intel.

It is installed in various Samsung laptops.

No, you haven't been ripped off.

I3 is just the processor and is built into several Samsung laptops.