Castle: (whistles) That's a lot of pemmican! (others look at him) A basic staple of the, ah, polar explorer diet. High in fat and protein, basically beef and grease kinda melted together into a jerky. You'd think it'd be disgusting but surprisingly... (stops as Beckett signals "TMI") I'll fill you in later.

Castle: Yeah, but for con men, it's not just about the money. I mean, for them it's about the game. The thrill they get from pulling a con, it's like a drug high.
Captain Montgomery: (walking up) Our con man was on drugs?
Beckett: No sir, Castle was just giving us psychological insight based on his extensive experience as a fraud.

Castle: ...And you believed him?
Ms. Schultz: Have you ever been duped?
Castle: I've been married twice...

Ryan: (laughing) You know those Nigerian e-mail scams?
Castle: Oh, Fletcher didn't pull one of those?
Ryan: No. It looks like someone tried to pull one on him, Fletcher conned the guy out of ten grand!
Esposito: That boy's good.

Beckett: Don't be so impressed, the guy was a criminal.
Castle: Ah, well, there's something about a well-played con, it just makes you want to tip your hat, though. And they have such great names, "The Spanish Prisoner", "Pig in a Poke", "The Pigeon Drop".
Captain Montgomery: I love a good time movie, House of Games, Catch Me If You Can...
Esposito: Ocean's Eleven, baby.
Ryan: Dirty, Rotten Scoundrels...

Title: Fool Me Once

The title is the first part of an old piece of folk wisdom, "Fool me once, shame on you. Fool me twice, shame on me." -- meaning "your duplicity is unexpected the first time, but the second time I should have been more cautious and wary of your motives, and not caught unawares".

Castle: And they have such great names, "The Spanish Prisoner", "Pig in a Poke", "The Pigeon Drop".

The Spanish Prisoner is a con from the early 1900s. In its original form, the con artist informs the mark that he is associated with a VIP who has been imprisoned in Spain under a false identity. The prisoner is concerned with the serious repercussions of revealing their identity, and is relying on the "friend" (the con artist) to dig up the money which will get them released. The con man "allows" the mark to supply some of the funds, expecting a generous reward when the prisoner is released. There is no prisoner, of course, and the only reward is the wisdom that comes from being had. There are many variations on this con which have been developed since then.

Pig in a Poke originated in The Middle Ages, when meat was particularly valuable, as were meat animals. The scheme entails the sale of a suckling pig in a poke (i.e., a bag). The steadily moving bag would, in fact, contain a cat or other valueless animal that was sold to the victim in an unopened bag. The scam is basically tricking someone into buying something without looking closely at it.

The Pigeon Drop is a con game where the mark or "pigeon" is convinced to give up a sum of money in order to obtain a larger sum of money, or more valuable object. In the end, the scammers make off with all the money, usually by switching containers.
Typically, it's in the form of a large sum of money purportedly found by a stranger (the con artist) who puts the money with the mark's money (usually in an envelope, briefcase, or sack) and possession of which the mark is then entrusted with. The money is actually not put into the holder, and/or the holder is somehow swapped with one containing nothing of value. In some manner, the conman or an accomplice makes off with the money, while the mark is left thinking they still have the money or object of value as "security" or collateral.

Ryan: (laughing) You know those Nigerian e-mail scams?
Castle: Oh, Fletcher didn't pull one of those?
Ryan: No. It looks like someone tried to pull one on him... Fletcher conned the guy out of ten grand!

Less improbable than it sounds. 419eater is a web site devoted to scamming the scammers (419 is the section of the Nigerian criminal code which deals with this type of fraud) (Warning! Potentially offensive use of language, particularly homosexual pejoratives). In particular, the tale of John Ademola, who the crew managed to scam into spending several hundred dollars of his own money, is detailed. T

he rules of Greed apply to scammers as well as somewhat honest people. Most of the people conned by scammers are people looking for the quick score in a get rich quick scheme. If you are wary of such offers, you are far less likely to get ripped off.

Beckett: Don't be so impressed, the guy was a criminal.
Castle: Ah, well, there's something about a well-played con, it just makes you want to tip your hat, though.

I concur with Castle, and offer a quote from noted SF author Larry Niven which applies:

I don't shoot a man for being incompetent in the Devil's work. I shoot him for being competent in the Devil's work. Admiration for his technique is part of the process.

One must study chicanery to prevent it. Appreciating skill with which chicanery is done is simple sense in recognizing a good, challenging adversary and not taking them too lightly. Regardless of the right or wrong involved, that is a metric regarding justice, and an important one -- but you need to respect your opponent's skills appropriately regardless of the justice metric, or they will outsmart you consistently.