Many of the concepts on the show are traditional cons that were prominent back in the 1930s. Unfortunately modern technology makes things much different. Why wouldn't a mark check the media and realize that there wasn't really a shooting where the crew faked one? How would the classic Spanish Prisoner still work given how interconnected the modern world is?
It's the equivalent of And Some Other Stuff. If they show workable cons, people will actually try them. The Spanish Prisoner is directly equivalent to the Nigerian Banker scam, and people fall for that.
Could also just be an example of both how good the gang are and how greedy the marks are; they provide enough background to convince a casual assessment for people who aren't actively expecting something like this, and let the mark's own greed do the rest.
They repeatedly say that you cannot con an honest man, yet actively DO con an honest man with short cons that have nothing to do with greed. Or, if argued that he's only pulled into them because of greed, then they're just as greedy and so claims it's not about the money rings hollow.
Not just short cons either - plenty of the long cons they run also are in no way dependent on the attempted dishonesty/immorality of the mark. In season 1 episode 2 and in season 3 episode 4, for example, they persuade the marks in both episodes to invest in bogus films. No perceived dishonesty or immorality is required by the mark in order to invest: they genuinely want to invest out of love of films/Bollywood.
It's heavily implied that the "can't con an honest man" rule only really applies to long cons - it's only ever brought up when the crew are working on long cons, never on the short cons - in which case it remains true, at least as presented in the series itself where it seems the vast majority of humanity is dishonest to some degree. All the targets of the various long cons the crew pulls throughout the entire series are decidedly not honest. Also, with regards to the short cons, it's again heavily implied (and occasionally outright stated) that the crew indulges in short cons specifically when they need to gather a lot of money very quickly and they're not just doing it for their own amusement. Thus, in these instances, it's not a case of "being greedy" (which is the state of wanting more than you need), but merely them getting as much money as they currently need in order to work the long con or use as a piggy bank. With a premise like this, there's always going to be a bit of fudging the moral high-ground when it comes to the smaller crimes but on the whole, the code they're shown to live by (that one cannot con an honest man) remains intact and, in several episodes, this issue is even lampshaded when it turns out they're the ones who ended up getting conned by someone else - they are not honest so, despite the moral posturing, they're not immune to getting conned either.
Mickey repeatedly states that he is not a thief. Ignoring that he is a con artist - thus is a thief, he's shown actively defrauding hotels, restaurants, and so forth all the time.
But by a strict definition, this isn't theft; he's not stealing anything from someone who's actively using it at the time.
The Season 1 finale features a past mark coming after the crew for revenge. When they confront them, it's pointed out that if they give him fake money, he'll just come back after them. They ultimately give him fake money & he finds out. What's to stop him from tracking them back down again and harming them?
This may be another reason why they left Britain for a time after that con; the man would have time to 'cool down' and focus on recouping his losses rather than try and get revenge on people he can't find.
It seems at odds with how notorious the gang (especially Mikey, Ash and Albert) are with how often they're not recognised. Could be Clark Kenting in action, except the gang keep to the same bar, to the point the individuals who have tracked the gang down know exactly which bar to find them at. And we do see a few times where the gang do get found, by cops or ex-marks, but these are painted as exceptions rather than the norm. There's moments where the gang makes plans to fake their lead guy's death to stop the mark coming after them, but usually a fake death only works (especially in the modern age) if you then remove yourself completely from your current life - not then go on to do more high end cons which sometimes involve making publicity material with the supposedly dead person's face planted on it.
To be fair, when the gang pull larger-scale scams they often focus their attention on different parts of society; cops might all be aware of the gang, but it's comparatively less likely that a crooked property developer who was conned years ago will be looking for art acquisition experts at the moment the gang are trying to con amateur collectors, as a random example.
