I've heard the claim a number of times that Crassus ran a protection racket—that his men would go to fires and demand payment to put them out, or even that they would demand payment not to set fires in the first place.

Every time a source has been provided for the claim, however, it has turned out to be this passage from Plutarch:

And besides this, observing how natural and familiar at Rome were such fatalities as the conflagration and collapse of buildings, owing to their being too massive and close together, he proceeded to buy slaves who were architects and builders. Then, when he had over five hundred of these, he would buy houses that were afire, and houses which adjoined those that were afire, and these their owners would let go at a trifling price owing to their fear and uncertainty. In this way the largest part of Rome came into his possession.

As I read the passage, it doesn't seem to suggest anything of the kind. Rather, Plutarch simply seems to be taking advantage of fire to purchase land cheaply.

No indication seems to be made that he had any interest in putting out anyone else's fires, whether they paid him or not—only in buying the burnt up land of those stricken by fire, and in acquiring for a song the land of those whose homes might burn down momentarily, or might not.

Indeed, I'm not sure that the passage even seems to support the idea that he fought fires at all, even once he'd bought the land. The slaves are architects and builders, not haulers of water.

The entire enterprise seems an ordinary predatory land-grab, rather than a fire company—crooked or otherwise.

So, my question is this: where does the idea of the fire protection racket come from? Is there a different primary source that describes Crassus' conduct differently? Is there a secondary source that misread Plutarch and has propagated a myth? Am I misreading Plutarch, or relying on a poor translation?