86%: Would you buy an IDS this good?

A number of commenters on yesterday's post, "Noh Entry: Halvar's experience and American Legalisms" are taking me to task for being idealistic about rule of law. I agree strongly with what Nicko wrote in the comments:

[C]ountries are at liberty to apply "complex, stupid, and complete arbitrary" rules but one of the fundamental tenants of the rule of law is that any rules should be applied consistently. It's naive to suggest that all travellers should be fully knowledgeable of all aspects of immigration law; that's an expertise for which people pay hundreds of dollars an hour.

Since this is sometimes an information security blog, I'd like to put this another way. Imagine you're testing an IDS that watches 7 identical packets flow by, and flags one of them. It either has an 86% success rate or a 14% success rate.

Without paying someone several hundred dollars, I don't know if Halvar got lucky 6 times, or unlucky once.

I do know that I'm upset that our border agents aren't consistent. If they were an IDS system, and that's all the data I had, I wouldn't be buying right now.