He'll be able to tell - The screw coil goes towards the bridge, and the wires come out of the bottom left corner (on all pickups I've used anyway :P)
And he'll probably check it with a meter first to make sure it's giving the right sort of resistance or whatever - and does it say in the packaging too?
:lol: Short answer is: Yes, he can probably tell...also, if you're only gonna change one pickup it's usually the bridge one from my experience :drink:
EDIT: And if he DOES get it wrong, you can always go back and say "I told you to put it in the bridge!!!!" - chances are he won't remember and would just change it for you