One of my favorite parts is the ability to kill the shopkeeper.
I usually only do it if he has climbing gloves, or a jetpack/cape.
If he has a shotgun in the shop, I just pick it up and shoot him. :D
The only downfall is that afterwards, every shopkeeper in the game will be after you, and your picture will be on a "WANTED" poster.
I usually get killed by them. :/