I made a Society6 account because I wanted to make t-shirts and I loved how much space they print on their shirts.
So I made a design and put it on a shirt and ordered it, but when the shirt came, the color was off.
I contacted their support and asked if they could check the file for me since the way colors look depends on the display.
They said the colors looked fine and sent me a replacement shirt.
The color on the replacement was perfect, however the lineworks were doubled, as if they ran it through the printer twice.
I can only imagine how prints and other products turn out since they obviously don't quality check.
As for RedBubble, I've heard nothing but positive things about it but haven't actually made and bought anything through them so I can't give my opinion on them