What attributes make scouts right when saying how much you need to spend?

A few years into an FM09 save my mate got might Marcel Desailly as a scout. Whenever he scouted someone and came up with a price required to buy the player, he was always right.

What attributes contribute to a scout knowing how much a player is worth to his current club?

And, if anyone knows exactly which ones, are there are scouts at the start of FM10 that are good for this use?

Thanks!