I have this theory that most decking boards are laid upside down!
The boards sold in the sheds have square grooves machined in one face like these
The photos here make it easier to understand;
This would be typical of UK sheds who often sell products without any knowledge of how they are meant to be used.
The boards I use are laid rib side up.
I think this has lead to the false impression that decking is slippery when wet or dirty. If laid square groove up they would be, your foot only contacts half the surface area of the board. Rib side up they are non slip.
Am I on the right track here?