there were no other people to witness the stupidity

I had to work my shift alone today, which isn't that big of a deal, but it did seem to bring out my share of crazies. The following is true, though their names have been changed because I didn't get them.
A man and wife came into the store with reasonably sane looks on their faces.
"Donnie": "Who's in charge?"
Now, right here they could be any number of things. See if you can guess: (a) Potential buyers, (b) Money collectors, or (c) Narcissistic Idiots. If you are reading this, you'll know that the answer is (d), Absolute Morons With Short Tempers. Let's see how long it takes those tempers to burn out, shall we?
Me (as I am alone and pretty much the senior employee anyway): "I am."
Muscle-Shirt Donnie: "Oh, great."
Faithful readers and/or people who know me will be able to visualize what's just happened in the time it took him to say Oh, Great: Donnie's stock has plummeted. If you're a jackass, I will probably not help you as much as I would. But anyway, back to the story.
Me: "Can I help you?"
"Marie": "Who's your manager?"
Me: "I am."
More shaking of heads. I can see that part of them is incredulous that some young kid is the head of this particular shift and the other part is thinking that they can push me over. Had they been nice before or had become nice as this goes on, I would've helped them out. But no.
They tell me what the problem is. I won't give you the line by line because honestly I don't remember it all, but I'll give you the main points.
1. Marie gave the store a list of books she wanted.
2. She went to Alaska.
3. Her husband, while she was in Alaska, bought two books for $4.80 each.
4. She already has those books.
5. "I don't read these kinds of books, I read car manuals."
6. She did not give us a list, she told us a list and some lady wrote it down.
Me (after #6): "When you give us a list, or however else we get a list, we put your name and number on the book on the computer and throw the list away." Of course this does not matter nor penetrate their skulls. They want us to be able to read their minds and to stop them when they buy multiple copies. The books, she tells me, weren't even on the list.
I realize that I'm shaking. I shake when people are pissing me off and I'm trying to keep my voice even. It's one of my less useful traits.
They go on about how they don't want a refund (then why are they doing this? I also hate it when people say they don't want credit or a refund or something of the sort, but they clearly do). They say a bunch of other stuff, and mention that they've called and talked to someone who said that they can't help them. Gee, I don't know why, they're so personable. Donnie goes out to get the books after I say that I'll look and see if we can take them for credit.
Marie echoes that they have two copies and don't need two copies and that he (her husband) bought the erranious copies while she was in Alaska. She asks for the owner's name. Every fiber in my being is saying: Say "What??!" very loudly and walk away or do something less pleasant. But what I say as steadily as my shaking will allow is:
"I don't see how this is our fault."
And her mouth drops open. I can see in her eyes that she would like to throttle me. She inhales to say something that would probably be unprintable. So I cut her off with:
"Fine, you want the owner's name; fine, here it is."
Meanwhile, Donnie comes in with the two copies of the two books. Did they think I wouldn't believe them? Whatever. I check to see if we can take them. Karma is sweet: not only do we already have two copies, but they haven't been sold since August 18th. I say that we can't take them, but they can try again some other time. Donnie laughs in that absolutely annoying way that people who are used to getting their way and suddenly don't and they don't believe it laugh.
And because I'm getting riled up just thinking about it, I'm going to jump right to the end.
They storm out and Donnie says "The word is out" like he's threatening to tell all his friends. Oh no, we're going to lose all of our key block-head demographic! I end up shaking for a while longer, but calm down eventually.
And...scene.