Although the details are a bit ambiguous, this question seems to focus on buying gems, and this question on selling them. What I could not find in either of them was a specific detail I'm interested in with regard to the sales process of commodities in general.
When you list a commodity, the game will "recommend" a unit sales price for that commodity. When using methods described in agent86's answer to the 2nd question, I can not determine any direct correlation to the "instantaneous buy price" or "10 sale average" price, and of course as he mentions the 24 hour stat seems bugged.
This "recommended" price often seems like a bad deal for the seller (if they are interested in profit), but I also suspect many sellers may just leave it as default - which is why I am very interested to understand how the number is generated.