This is one area that took some time for me to get my head around. Essentially, you need to realize that with Scouting on, you see everything through the eyes (skill set) and personal bias (tools emphasis, etc.) of your team's Head Scout. Not too hard to grasp. But here is the kicker-
the exact same parameters apply to every other team and their Head Scout.
So, hypothetically, if your Head Scout was a perfect+ evaluator across the board, he would still have some randomness with regard to players due to his scouting style bias. Most of us never get all that close to this anyway, but it's worth noting that when you are in negotiations with other teams for a trade or have a player on the block, consider that their Head Scout may over or under value a player, whether yours or theirs. It cuts both ways, sometimes you get a great deal, other times you scratch your head wondering why teams don't pounce on what you deem a steal for a player you don't have room/need for and want to move in a trade.
It is a major reason why at times the AI seems goofy, but I think this is mostly due to the effects of each Head Scout in your league. Personally, I wouldn't want it too predictable.