It's pretty similar when writing content. Scope creep tends to be real across almost every industry. "You did this for me, so now do this, this and this. You want to be paid extra? No way." So that's not unique to SEO.
But I do find that I don't have to educate my clients when they're paying good money. They already know what they want. And if they don't, I will give them some suggestions. They almost always listen to me bc they trust me. When they don't it's not a big deal. 99% of the time they mess up, and then they pay me to fix it anyway.
However, within the scope of content, fixing a client's mistake is much easier than fixing a client's SEO mistakes. Rewriting something takes a couple of hours and the results are almost instant. That's not the case with SEO.
