Interesting, just had this idea - would it be possible to feed the model with wrong data and make it giving bad suggestions to competitors who opted in?
Ha! Yes to some extent it would but that would really mean either a) we decided to run recommendations using a sparse model or b) we never validated the data or kept a watch on models when they were trained/retrained. This type of manipulation is typically likely when you're much larger and have alot of bots involved on the platform.