In a perfect world where everyone was totally honest, yes that would be the thing to do. Not having taken the test myself I'm not actually sure how taking the OOPT works, but I'm assuming it would be fairly easy for someone with less than honest motives to lie and get someone else with a C2/native level of English to sit the test for them if they wanted to. That would seem to be a rather substantial issue here.

Your encounter with that student is actually rather interesting, because I can't help but wonder whether the student was actually asking about your English proficiency. I actually have a slightly different interpretation of what she may have meant when she said 'real English.' The reason for this is that I've seen that some students on this website have the impression that native English speakers use language with each other that is far removed from the things that learners are taught in the classroom. 

In some ways this is easily understandable. Native speakers will generally speak much more quickly to each other than they will with someone who they know is learning the language. The variation in accent that you will hear in real life is certainly a lot greater than what you are exposed to in a classroom. The pronunciation will probably be more lax (or just plain lazy at times) and there will be use of slang/idioms. I suppose if you are not familiar with this manner of speaking, the first time you come across a native speaker it may all feel rather alien. And perhaps it was to this that she was referring when she mentioned 'real English' to you. Or maybe I'm barking up the wrong tree, who knows...

I’m with Aegis — more than half the “secrets” in those articles wouldn’t even be understood in the US (or anywhere outside of England). I can just imagine an A2 or B1 level ESL student delivering those lines with a heavy foreign accent and non-native grammar — thinking they sound like a native speaker (as promised by the author).

If you’re a native speaker or a learner at a C2 level, then maybe, just maybe, you might want to add some of that to your passive vocabulary — but I would wait until you’re actually on a flight to London — preferably within sight of Heathrow Airport.

As I always say, if you learn standard English, you’ll be able to communicate anywhere. Until a learner has learned a few thousand of the most common words, every moment spent learning regional expressions is a moment wasted.

I am with Paul. I think this student was not questioning your English proficiency. Google 'real English' and spend some time surfing the language teaching or language learning related sites you will get. You will be surprised how well this new motto sells online! You will also find the concept is being used on italki.

Actually, Michael, I’m with Paul and Marta.. I think your student saw you were from Southern England and was hoping you could teach her cockney rhyming slang. Sadly, there seem to be some unscrupulous hucksters out their who are selling students on the idea that English teachers are "holding back" some sort of "secret knowledge."

You wept? I assume that was a joke.

I'll back up what Phil said. A few months ago there was another Brit who wrote a couple learning articles here, both focusing on "real english - what your english teacher won't teach you". There was a lot of stuff that just wasn't standard, especially in the states. Several students made comments like "finally, someone is telling us the truth, unlike those anal teachers who want us to speak in an obsolete/formal manner". It was wierd to follow the discussion, because there was no convincing them otherwise.