How to detect a sociopath

I’ve learned some great insights into human nature from spending a lot of time interacting with people on the web. You know how, whenever they interview a serial killer’s neighbor on TV, they always say “He seemed so normal!”? Well, online you can tell these people are crazy if you picture the back-story for the things they write.
Let’s find an example! Imagine you run a little bed and breakfast. (I don’t know the owners of this particular place, but they seem to be fairly well regarded.) Some random guy calls you up, and he says he and his wife have an expired gift certificate for a stay at your place — is that cool?
You’re a rational small business owner, so you apologetically offer a negative response: “I’m sorry, sir — we can’t honor a certificate that’s expired. Thanks very much for calling, and I hope you’ll join us sometime.” This sort of thing happens all the time, so you don’t think much of it.
But the guy calls back. “But we’re coming during the off-season! Doesn’t that mean you can honor our certificate?” “Sorry, the expiration date is really what we try to go by… and we don’t really tend to have an off-season, things are busy all the time. But again, thanks for your enthusiasm.”
There’s another call a few hours later, and caller ID shows the same number. You’re tending to your actual customers, so you ignore the call and let it go to voice mail.
The next day, the guy’s wife calls. “Okay, what about one night? The certificate’s for two nights, why not just give us one?” Understandably, you’re getting a little annoyed. “Ma’am, this isn’t a negotiation. We have a standard policy that we follow so we can be fair to all our guests. I’m sorry you weren’t able to get here before your certificate expired.” She starts shouting, so you excuse yourself and hang up the phone.
A few more calls from the number, and now you’re letting them all go to voice mail. There’s something on one of them about “What if it’s in the middle of the week?” but it’s incoherent.
Some time passes. You think the whole thing has blown over. Maybe those cheap bastards actually went somewhere that they had to pay for and had a good time. So you’re cruising around the internet, seeing what the buzz is about your little business. And you stumble across a review:

We were given a gift certificate for two nights that we were unable to use within the one year time period. The proprietors were unwilling to accommodate us, even for one night in the middle of the week during the off season. They avoided our phone calls, did not return phone calls, hung up on my wife, and yelled at my wife. This is the most unprofessional “business” I have ever encountered. This discourteous treatment cannot be justified.

As a public service, I offer you my analysis. This quote is how you can tell this guy is a sociopath. Not that he merely went online and vented to random strangers about his greediness. No, rather, that he was willing to concede his own willful ignorance (or illiteracy?) while complaining. The web is littered with these chuckleheads who point out their own sociopathic behavior while complaining about others.
WandM_alum, you ill-tempered bastard, I salute you! You have somehow reached the same age as me without tempering your sense of entitlement one bit since you were a 3 year old throwing tantrums. And I must disagree with your conclusion: This discourteous treatment can absolutely be justified. Because your ass is crazy.