Apparently there's some ancient etiquette for traveling men and prostitutes that the Secret Service neglected, to their doom.
When I worked on ships, seamen were a superstitious lot. When there was a bad storm, while the ship pitched and rolled, the crew, unable to eat or sleep, would gather in the messroom and grumble. Anyone who remembers Coleridge's ancient mariner knows that seamen don't blame the wind and tides for bad weather and rough seas. Rather, they blame a fellow member of the crew -- someone who has, say, killed an albatross. During storms, they'd mumble darkly that a crew member had "Jonah'd" the ship -- done something wicked, while ashore, that caused the seas to rise up and take revenge.
Inevitably, someone would point out that the likely cause of the foul weather was that one of our crew had committed the worst sin of all: not paying a whore. All would nod gravely. In my day, seamen were convinced that this was such a serious infraction it could threaten a ship's survival. More than once I saw fellow crew members, who'd come back to the ship so drunk they couldn't remember where they'd been, make superhuman efforts to send money to a woman ashore in a desperate attempt to avoid the curse of the unpaid prostitute.
I thought about this while reading about the scandal in Cartagena. It appears that getting drunk and going back to the hotel with the women wasn't, in itself, what got the Secret Service personnel into trouble. What got them busted was that someone in their group refused to pay an escort the pre-arranged price. One of the escorts wanted $800. She said that a Secret Service agent offered her $30. (To put that figure in perspective, it's more or less what seamen used to pay in Cartagena 45 years ago for all-night companionship.)
Seems pretty obvious: if you don't pay for services rendered it's going to eventually catch up to you.