This was found by phoenix-force411 on Youtube.
https://www.youtube.com/watch?v=mS-G7gPaWqo
Description:
This glitch applies to ACII, ACB, and AC:Revelatons.
How to do it:
Before entering the store take your weapon out(Crossbow, short blade, or sword), but make sure Ezio's hand is only in the animation of reaching for his weapon. As he reaches for his weapon, enter the store and select a weapon according to the weapon you are trying to get rid of. For example, if you're trying to get rid of the sword, select another sword from the store. Once you've selected your weapon, exit the store and Ezio will take his weapon out only for it to fall to the ground.