Craigslist:
* Listings have "ASKING" prices and can easily negotiated down 5-20%. So even if you provide a historical information of "Asking Prices", its still not a 1-1 relationship to how much you expect to sell your item for or its "BUYING" price
* I do question the value of historical information on CL: Its never been available, therefore neither buyer nor seller expect it and their view of the marketplace is limited to the time they hit search. And it is this view that they will use to determine a good price for an item. When I need to buy something that I need NOW, I try to choose the nearest, cheapest item, satisfying my requirements that is CURRENTLY available. Historical information doesnt come into play.
Ebay:
* Since I already have access to historical information(completed items) and I can use it to figure out how much to sell my stuff for, I dont see what Priceonomics bring to the table here.
Again Im trying to figure out where you guys are going with this. From technology standpoint, all this content scraping, indexing and searching is interesting, but what problem are you solving and how do you plan to make money with it(short of arbitrage of aerons)