Did Obi Wan tip the bartender in the cantina after he killed the death sentence dude and cut off the other guy's arm? He made a bigger mess than Han Solo did after all.
He didn't start it. Han shot first so proper etiquette dictates that he should tip the guy for the mess.

Han was defending himself - Greedo was monologuing but was going to shoot him. Besides, you always tip your waitress if she has to pick up a mess at your table, even if you didn't make it. Actually, it's worse - I don't even recall Obi Wan ordering a drink. So that old fart goes in, conducts business, creates one corpse and one bloody, severed arm, attracts Stormtroopers, and doesn't buy a damn thing. AND, he doesn't tip. Poor form.