I'd say it's fairly common at low level, simply due to the lure of all that PHAT LOOT! But as you go in level there's fewer and fewer ones.
In my campaign we, a 6th level group, recently encountered a group of level 1 wannabe adventurers... the party's Paladin, our leader, then hired them to go on a sidequest we didn't do and asked them to go meet us at our base of operation afterward. The side quest, to recover a signet ring, was completely superfluous because we just stole the map we were supposed to get in exchange for the signet ring! AND the guy who asked us was probably thrown in jail, or executed, for corruption not long after (it's complicated).
In a following session we ALMOST hired a Goblin and Bugbear bandits we had defeated to track that party down and see who would come up on top, but we ended up killing the Bugbear and employing the Goblin for something else.
All in all, an hilarious event.