From my view the biggest question I sit with regarding this experiment/overly sales number focus/the search engine in general:
Why would you use the same sales strategy for music and wordpress themes for example, or any of the other markets for that matter? It’s such different worlds and surely it must be worlds that needs specialised experiments? Some products are more timeless, others not so. Ratings are interesting in some markets, others not at all.
Just because your living room is awesome with a carpet floor, does not necessarily mean your bathroom should have it too?
How about hiring some more specialists for each market? Could that be an interesting and lucrative investments for the markets in the long run?