I've been around a bit -- recording and editing voice-over sessions, doing original sound designs for plays and musicals, mixing a live band or two, working as a house technician for comedy acts and dance and multi-media. So I could say I have a list of warning signs for when you are going to be dealing with a Client From Hell.
But here's the rub; you always are. The expectations of what can be accomplished with sound are almost always wrong. The client will never accept the time it will take, the equipment needed, and what it will cost.
Be that as it may.
"I know sound." -- they don't. The people who actually know what the hell they are doing never say this. They don't talk the talk; they walk the walk. Really, everyone will try to tell you they understand the sound better than you do; the "I know sound" people are simply a wee bit more arrogant and even harder to understand (as they insist on phrasing everything in terminology they only think they understand.)
And related to that:
"I know what I want, I just don't know the technical terms." -- they don't. They are using this supposed lack of a common technical vocabulary as a shield to protect them from having to admit that they don't know what they want. Technical terms apply to technology. They are paying you to work the technology. It is, absolutely and explicitly, your job to figure out how to implement their creative needs. Using technical terminology is an attempt to dictate the tools and processes for you, constraining your work and cutting both you and the client from the ability to realize the creative goals.
This phrase is also a signal of another related attitude:
"I don't know what all those buttons do but..." -- what this really means is "Your job is so simple I would be doing it myself if I had the time." And they are wrong. Their first mistake is assuming that the tough part is figuring out "what all the buttons do." No...that's the easy part. Where skill begins to come into play is understanding why and when to use those buttons.
"Show me something and I'll see if I like it." -- means they have no clue how much time this takes. Yes; in a perfect world (and there are such worlds, I've been there. Rarely) you can indicate directions with a sketch, get that approved, purchase materials/record tracks/whatever, get the rough approved, polish that up into the final cue or mix or setup. Reality is that it takes skill, a lot of skill, to intuit from a smaller clue like a single microphone being soloed or a rough sketch of an effect what the final mix will sound like in context. Reality is that the client will focus on all the rough edges, forcing you to do time-consuming final-quality work before they reject it. These are, yes, the same people who will solo a single instrument on stage and tweak it forever with absolutely no grasp of what it will sound like seated in the final mix.
And, yes, within those conversations is usually invoked:
"I can tell just by listening..." -- no they can't. No-one can. Every seat is different, every performance different, every set of speakers different. The actual cue or mix in show conditions is a minimum, and then it much be heard from as many different parts of the house as possible. But then, these are the same people who will critique a mix from on stage.
Here's a few slightly more subtle ones from the world of FOH (aka music performance). Lack of a tech rider. A poorly constructed tech rider. The best ones are when they give you a printout of an email that has been passed through a dozen levels of reply in a chain of Chinese Whispers that finally drilled down to something like, "We need four microphones."
The band arriving half an hour before showtime. Surprisingly common. It is a given that said band will have a completely different line-up than what the client had been describing up until that moment. And inevitably, that same management drone will grab you away from the very moment you are greeting the band with a "Can we have a Sound Check in...?" (insert original schedule, before the band ran late).
From live theater, "The guy who used to do our sound." Someone was there, they might have even known what they were doing, but they were kicked out without notice and left no documentation, and all the things that needed to get repaired, restored, or returned after the last show didn't. And no-one even has the keys -- but the client still expects at least the service they had last show; as a baseline, with the newer and better sound tech building upon that with all the skill they aren't actually paying you enough for.
Inspired from reading at a website of stories by the same name. My last two or three clients were all wonderful to work with and I had no troubles with them.