Originally Posted by
shadow_archmagi
Simple solution: Present the money as being a tool that solves problems.
IE: "Homeless man, you're going to have to pay your guild dues by climbing to the top of the Shard of T'charr and setting up this magic antenna so our listeners on the far side of the continent can hear about today's airship lacrosse results."
"What if I paid in money?"
"You have that!?"
Of course, once adventurers hit high levels this becomes meaningless, but as has already been said, the idea of normal people forcing them to do things is like the idea of the Gondor sending out the DMV to stop Gandalf from riding around without a license.