They hired you as an expert.
Lesson 4 is a bit of a two-edged sword. On the one hand, you should never say anything you do is easy. You're an expert and have invested thousands of hours to learn a craft - what's easy to you is still an insurmountable challenge to others.
At the same time, clients will often try to lessen your expertise; if what you do is actually easy, then it should cost less for you to do it.
Every time someone asks me what I do for a living, the next phrase out of their mouth is often, "oh, neat. My 7 yr-old nephew does that too." Trying to build a business relationship - one where my time is respected and adequately compensated - becomes nigh impossible if that's where the discussion ends.
Instead, I'll respond with something along the lines of, "oh, he wants to get into this field, too? That's incredible! Have him give me a call and I'll pass along some tips for classes he can take in high school and college so he can get started on the right foot. This is a challenging industry, and he'll have an easier time breaking in if he knows where to start."
With rare exception, there is no 7 yr-old nephew (or niece) who can do what we do.
Unfortunately, so many client managers will know a kid[ref]I use the term here to paint a specific dichotomy between a youth who "builds websites" and a young web developer. I know many talented developers under the age of 21, and I bristle when colleagues call them "kids." It's belittling to refer to any of our contemporaries with child-like terms.[/ref] whom they allege can work at the same level we can. This is a fallacy that's nearly ubiquitous in our industry, and it has some serious consequences.
Until they truly know you, a client won't trust your judgement.
They hired you as an expert, so you need to act like it. Offer expert opinions - even when the opinion is "no, that's the wrong way to do it."
Pushing back on client feedback is difficult, but necessary. They're not the expert developer - if they were, you wouldn't be working with them. Their teenage kid isn't the expert developer - if they were, you wouldn't be working for them. The article they read last week on whoever's blog, though they might be an expert, is not the hired expert developer - if they were, the client would hire them instead.
When you speak to a client, speak from an expert position. If you flat don't know something, explain you need some more time to weigh the alternatives before making a recommendation - never say "I don't know." You're an expert and expected to make expert recommendations. Saying you don't know just reinforces the belief that the company intern, the boss's daughter, the fly-by-night blog know more than you and that your judgement is flawed.
They hired you as an expert. Behave as the expert you were hired to be.