Spartan Mercenaries

Hello EB scholars and fellow forum goers!

Seeing as this forum is a repository of all things ancient and arcane and because this is a question I've had rattling about in my head for quite a while now, I've decided to post it here in hopes of recieving an answer.

How was it that Spartans were able to hire themselves out as mercenaries? I was under the impression from what little knowledge I possess that once their agoge training was complete, Spartans were under obligation to serve the state until old age. Were these mercenaries lent out by the state for profit, or were these bands rogue Spartans who had forsaken their homeland for gold?

While I find my latter speculation rather iffy, I can think of few other scenarios that would prompt a full blooded Spartiate to leave Lakedaemon.

Artificer