I like to put in my 2 cents and Im not sure if this was mentioned in this long thread, but in addition to this suggestion I think requiring buyers/sellers to type in a comment when paying would make things so much more convenient.
And what I mean about commenting is that a buyer/seller should type what they wrote/bought so that each party has a convenient, easy to find record of what each transaction details.
For me, I would sometimes go through the records and look for certain items that I sold in the past and compare the price with the current price. That, or I need some sort of reference on pricing. Basically, things of those nature.
I know some people dont even bother to make a comment, but if they are required to make one, they'd probably be more inclined to type in what they exactly sold/bought.
This is a long shot, but hey, its a suggestion.