Like many LSAT questions, this one is trying to trick you by giving you way more information in the argument than the conclusion actually depends on. Instead of the text describing some fake scientific “facts” or a bullshit study, it starts you out with a different claim, by advertisers, about how qualified Ace's plumbers are, based on their difficult certification process. Note that the conclusion sentence begins with “Plumb-Ace plumbers may or may not be more qualified” which tells us that the conclusion takes no position on actual qualification, focusing instead on the other item in the equation: the “difficult” certification process.
The idiot claims that because almost everybody who takes the written portion of the exam passes it without difficulty, the whole process is easy. Now, we don't know anything about what the certification process looks like beyond this alleged written portion. What if the exam is like the LSAT and the writing portion is the least worrisome section of an otherwise challenging test? What if, you know, the plumbers have to fight a dragon before they take the test as part of the certification process? We do not know enough about the process to buy the assumption that the written portion is indicative of the entire test.
Let's look for an answer choice that points out that one portion of the test does not prove anything about Plumbing-Ace's larger certification process.
A. This answer describes the LSAT's most common flaw, confusing a sufficient condition for a necessary condition. If that flaw would have been present in the given argument, I would have seen it. It wasn't there.
B. The argument is actually anti-certification, not pro-certification. This answer describes the exact opposite of what actually happened.
C. The text never mentioned anything about any plumbers outside the region, and it doesn't matter anyway, because the conclusion only cares about whether or not this certification process is difficult. Even if they existed, outside randoms wouldn't affect that.
D. This answer describes a flaw that sounds like this: "Because you tried to reach the moon on a bicycle, and failed, it is therefore impossible to reach the moon." That's bad logic, because there are other ways to reach the moon just as there are other ways to prove that a plumber is qualified. But that's not the flaw that was present in the given argument.
E. Here is our answer, and it's really pretty obvious. The only hard part was getting past the other answers, which was a whole lot easier because we were armed with a strong prediction. The argument claimed that just because one part of the certification process (the writing sample) was not difficult, then the whole process must be easy. That's bullshit, that's what we were looking for, and that's exactly what E describes. So this is our answer.
From Mollie: Though I have been thinking about it for a long time, I decided it was time to go to law school just a few weeks before starting Nathan's class. I work with children and I'm non-profit junkie, which means that writing and talking about my feelings are my top two skills in life. Thus, studying for the LSAT was like opening an entirely new chapter in my brain. Thanks to long hours, and Nathan's help, however, I am getting much better, and enjoying myself more than I thought I would.
Please ask questions and/or suggest corrections to anything that seems confusing... we want to make this the best resource we can for LSAT students. We'll have all the June 2013 explanations up as quickly as possible. Thanks for reading. Tell your friends! --nathan