They can have all sorts of one time Arrows they could sell: Arrows: Paralysis, Petrify, Iron, Steel, Poison, All Elemental Arrows ( Wind/Fire/Ice/Earth/Light/Dark/Water <--- These can be chargable arrows but the arrows themselves are 1 time),Darksteel, Slow, Sap (Hp Drain effect) and so on and so forth.

The Possibilities are endless, If done right this can be a great system to do.

Types of Arrows:

-Regular
-Debuff
-Enhanced arrows (if they would have alchemists enhance the arrow, which the enhanced effect would fizzle in time and have to go back to an alchemist to get them recharged) aka Elemental Arrows.
-Light Arrows ( Less damage, faster AA)
-Heavy Arrows ( More damage, slower AA)

I could go on but this what I think they should do if they go this route.