A - To avoid confusion when collecting our money. Let's us know what we actually sold
unless your selling stuff for other ppl, it's all your money so this point is moot.

B - For gatherers helps us determine what our stuff sold for, this helps us determing what to list our next item at.
at first i agreed with this but it would only work if you listed the same item at diffrent prices otherwise you would just raise the price until the item stop selling then you would know what the price cap is. sadly making this point moot too.