Just to clarify what's happening. You're showing the customer the weapons they want (1H-Hammer). They then look at the closest weapon to them (Polearm), and take that instead.
To avoid this, make sure there are no other weapons closer to them than the one you're handing them. Even better, as customer won't yet pick weapons off of selves when they arrive (Bug 2), you can keep your weapons further back in the store until needed.