So tell us how that would work.
I'd use it as the foundation for two concepts. First, by hiding your true cert level, you are not being truthful and if you are not truthful to the dive op, then you won't be truthful in a lawsuit where you have something to lose. Second, you hid your true cert level because you didn't want to shoulder your responsibility as a diver of that level and in fact didn't shoulder it.
One of the ideas for a lines of questioning was that if I asked you your age and you gave me a number that was less than your real, current age, that would not be true, even though you had once been that age and had advanced past it. So how is it different if I ask you your cert level and you tell me something that you have already advanced past:
Q. What is your age?
A. 52.
Q. If you said 42, that would not be true, right?
A. <insert answer>
Q. It would not be true even though you were once 42, right?
A. <insert answer>
Q. At a minimum, saying 42 because you were once 42, would be misleading?
A. <insert answer>
Q. In fact, it would be intentionally misleading?
A. <insert answer>
Q. So, how is saying you are AOW, when you are actually an instructor any different?
The beauty of this is that the answers are not really relevant, though a very well prepared witness could probably come up with answers that might downplay the issue.
As far as avoiding responsibility, I'd go after the reasons one might have for not disclosing their true cert level:
Q. Why didn't you disclose that you were an instructor?
A. I did not want to get buddied up with an inexperienced diver because it would take away from my enjoyment of the dive.
Q. Did you think that if the op knew you were an instructor you'd be buddied up with an inexperienced diver?
A. I was concerned about it.
Q. Do you think it is more or less likely that you'd be buddied up with an inexperienced diver if the op knew you were an experienced diver compared to an inexperienced one?
A. I was concerned about it.
Q. What would you have done if the op had said: "You two dive together because you are both inexperienced?"
A. I'd have asked for a more experienced buddy.
Q. You'd have said: "I want an experienced buddy even though I'm inexperienced"? Or would you have said "I'm really an instructor and want to dive with someone my level"?
A. <insert answer>
Q. So, if you had initially disclosed your cert level, and you'd been buddied with an inexperienced diver why couldn't you have said the you want someone your own level?
A <insert answer>
Q. Isn't it true that you did not disclose your true level because you were worried that if something went wrong, people might be looking at you?
A. <insert answer>
Q. In your mind, you thought that as an instructor you had supervision duties beyond what an AOW diver would have?
A. <insert answer>
Q. You were on vacation and had paid a lot of money for this dive?
A. Yes.
Q. And, you didn't want to waste it by having to be responsible for anyone -- isn't that why you lied about your cert level?
It is important to remember that even of the lawyer is not a diver, it is an easy matter for a lawyer with a significant case to engage the services of experts (some of whom are found on SB) to help them figure out their cases and angles of attack.
I hope this helps somewhat.