Interesting, solves a problem I have. Although as I do not live in the US, I don't have it often.
I wouldn't include books at all in the lists. When I want someone to help me discover great products, I don't think about books. You will have a strong bias for the taste of your current visitors and also there are other, better ways to discover books.
But to discover a "water garden fish tank" that's the problem I have.
Currently for the MVP we are not doing anything fancy, the 'hot' list is ordered (desc) by number of upvotes and 'trending' is nearly the same as 'latest' except limited to last 7 days. We will keep monitoring and keep either 'hot' or 'trending' in the future. We want to keep the ranking of each product simple and based on what people are upvoting, so there won't be any hidden scoring.
I wouldn't include books at all in the lists. When I want someone to help me discover great products, I don't think about books. You will have a strong bias for the taste of your current visitors and also there are other, better ways to discover books.
But to discover a "water garden fish tank" that's the problem I have.