Spot on what Jono said.
i.e. if you saved your game on the ingame date of 1st July 2012, and you load that in Genie Scout. But you continue to play the game to 1st August 2012, without saving the game and reloading it in Genie Scout, the sale value prices could change massively.
Another thing that could push the price uop when compared to Genie Scout is rivalry's. If Manchester United wanted to buy Gerard for example, the price Liverpool will want will be more than, say Barcelona wanted him due to the rivalry.