Single-speed freewheel installation question

I haven't yet ridden the bike, because :
a) I got the bike assembled today
b) I am not sure that planetX will accept the wheel set back if it's used.

I'm pretty sure my mechanic picked the correct side (if there is any difference) because he is supposed to be a scpecialist on old bikes, restorations fixed etc.

To clarify, my suspicion is not that he's picked the wrong side of the hub but that he's put the face of the freewheel that should be outwards towards the hub. You will notice this very quickly if it's true!