Is this some kind of new phenomena? I’ve sold several thousand bucks worth of stuff lately on craigslist. It’s mostly been an easy pleasant experience, you give me cash I give you stuff. But lately we have been getting these retired folks who come over, look at our $40ish item, then talk and talk and talk, tell us their whole life story and then finally say…well it’s not what we wanted. WTF??? Do I look like a priest or a friend or what? Buy it, don’t buy it, don’t waste my time.
I get that you feel your time is/was wasted, but I don’t think some idle conversation makes them a nut job.
They’re casing you.
You or your body parts.
They’re harvesters.
So, they just need someone to talk to. Each time one of them turns up, get their name and phone number. Then pass on the names and phone numbers to the next ones that turn up. That means that they can talk to each other.
chances are they’re garage-sale aficionados who have moved on to CL. These people don’t have a single thing in their houses which they paid more than $1.25 for, and they’re sure as hell not going to change their ways just for you.
I’m getting a Jeff Dunham’s Walter, the grumpy old man as a Walmart greeter vibe here…
Welcome to Walmart. Now get your shit and get out.
One trick is to tell 'em stories that don’t go anywhere - like the time I caught the ferry over to Shelbyville. I needed a new heel for my shoe, so, I decided to go to Morganville, which is what they called Shelbyville in those days. So I tied an onion to my belt, which was the style at the time. Now, to take the ferry cost a nickel, and in those days, nickels had pictures of bumblebees on 'em. Give me five bees for a quarter, you’d say.
Now where were we? Oh yeah: the important thing was I had an onion on my belt, which was the style at the time. They didn’t have white onions because of the war. The only thing you could get was those big yellow ones…
If you know anyone in sales they have a variety of “exit methods” to politely bow out of such things.
One thing you may want to do is ask them when a good time is and when they arrive, mention you only have 30min before you need to go pick up wife, kid, ferret at yodeling lesson, whatever.
Smart phones can also be easily set to alarm after 15 min, giving you a handy excuse for a “fake” phone call, “oh you are done early?, ok honey, be right there”
That’s fine, as long as they shut up.
These must be the same guys who linger around the Y lockerroom ready to pounce on the slightest sign of interest so as to talk your ear off about whatever Fox News has told them to be outraged over.
Usually, you can avoid it by not making eye contact. Kinda like panhandlers.
If that’s not possible, interrupting with something wildly inappropriate will usually shut down the nonstop stream of blab – tell 'em you’ve got to go get started on prepping for anal sex, or that you forgot to take your antipsychotic meds, or something.
Now, my story begins in nineteen-dickety-two. We had to say “dickety” 'cause the Kaiser had stolen our word “twenty.”
I tried the “stare intently at his left air and swat an imaginary fly” at the psychologist during my concription evaluation to quickly end that discussion. 
When they start talking, turn back to the house and shout real loud, " I said shut your trap, woman, or I’ll come in there and give you the goon hand!"
Maybe finding a couple extra WatchTowers to pass out might help.
Thanks for the hints. I was just about at the end of my rope with the last couple. They were retired ministers, didn’t try to recruit me or the door would have been slammed. Called me 5 times about the item I was selling, the last to tell me they were stopping at a fast food restaurant on the way over. Why?
They arrived after 8pm and checked out the merchandise and then chatted for over 30 minutes before saying it wasn’t the right color. Never once asked about the color in the previous 5 calls. Then called again after they left and asked what color our walls were painted???
Silly me I was initially more concerned by the guy whose email was Voldermort.something who came over to buy $600 worth of stuff. He came, had the cash in 20’s and left within 15 minutes.
Dammit, I knew there was a reason we shouldn’t have packed the anal sex book first.
I had one guy show up to buy a Yachtboy radio. He immediately mentioned the hallowe’en decorations out front and asked me if we planned to put up a nativity for christmas, “cuz that’s what it’s all about, ya know”. Then he prattled on and on about his old friend who he convinced about Jesus and then managed to scam a bunch of ham equipment off of him that was worth a whole bunch of money. At least he bought the radio.
“You’re making the metal plate in my skull vibrate. And that’s when bad things happen!”
I remember seeing a comedian on TV once talking about how old people look for excuses to talk to someone and they’ll say anything. He said that he was on a bus once and this old guy sat down next to him and asked, “Where you from, young fella?” The guy replied that he was from Chicago, to which the old man replied: “Ahh, Chicago. I’ve got family in…San Diego!” 
Maybe you need to improve the descriptions of the shit you’re selling, or better yet, include a picture. Save yourself some hassle.