When I was building the search for a big ecommerce books site (approximately 20 million products), it was a nightmare trying to filter the print-on-demand produ

When I was building the search for a big ecommerce books site (approximately 20 million products), it was a nightmare trying to filter the print-on-demand products. At the time they were creating new "publishers" on an almost weekly-basis, we were constantly having to tweak our blacklists. The big problem was caused by the titles of all these books being stuffed full of keywords, so for almost any conceivable search they would show up quite prominently. There were some technological solutions we implemented, but it was a major annoyance all the same.