They're not intelligent to understand the game is my point.
They've seen countless matches and could see a million more but will never have the underlying intellectual capacity to properly understand football.
Their success is a result of them having been genetically predisposed to kicking and chasing a football at a higher level than most.
The answer is hundreds of hours. The amount of footage and data collected on a player or team and analysed is somewhere between 95% and 400% of the scouting.
Then they go and watch a match or two - much of the importance of which is being in the same physical place as the player, his agent, his current owners, etc.
So I'm fairly confident that if multi-million £ football teams can make multi-million £ judgements via footage and statistics, with the odd live match thrown in here and there, then I can base my opinions on the same.