Are Game Used Cards Real or Fake?

To anyone who would like to respond:

In the past I have bough certain cards for resell later but I've
always been
skeptical of game used cards and autographs that come out of packs so I have
never built a personal collection .I've seen cards with wrong color swatches
and mass produced autos and I wonder if they can be real. I'd like to know if
I'm just being paranoid about this. Feel free to email me with your thoughts.

Venom