I finished my Lego lambo yesterday and discovered I put one of the diffs backwards. Now the front and rear wheels spin in different directions when you try to push it. Ah well, it's a display model and no one else will ever know.
I bought the Fast and the Furious Lego sets and they're just display models tbh. So in one way it's good that you don't actually have to use them for play. But like Calhoon said, it would be annoying just knowing that it's not perfect.