Look, I can't speak for BBB, but as someone in software development, it's not a big challenge to write software that will track every bike transaction on eBay. Why would you think BBB doesn't do that? Cross that with putting a 'bot on CL, check prices on used inventory posted on LBS sites... this ain't quantum computing. Harder questions are: does source make their pricing methodology transparent? If prices are questioned, can they be qualified and possibly updated? How often does a given model trade and price? Else, you're likely just using a standardized depreciation rate, and a seven-year-old anything is technically toast. Except a Babe Ruth baseball card, right?
I used to work with pricing in the bond market, same kind of question when you're looking at "over the counter" transactions. "My price is better, yours is wrong." Yeah, heard that a bazillion times. At the point of sale, it's two parties negotiating and we'll see who wants the transaction more...
But spare us the venom. That price is worth what you paid to get it. On the internet. yeah. But, gotta start somewhere...