Also, there's arguably a market in titles - I know I've missed stories of interest to me, because I didn't recognize that aspect of them from a specific title.
4) [I believe] the site matches URLs, but doesn't catch non-significant differences, because it's difficult to tell what's significant. e.g. in this case, the previous submission's URL had an appended: ?tid=true
5) [I believe] there is a HN list with a slower decay, so it's averaged over a longer period of time (like Digg's "Top in ..." on the RHS): http://news.ycombinator.com/best but it's not very newsy, because it's averaged over a longer period of time.
With your friend, isn't the asking price also an input? The experience of getting more sales when you increase prices is not uncommon.