Nothing surprises me at this point. I've seen melted scanners that someone tried to modify, and cars with scary unsafe "enhancements", so..
In 1965, we bought a house built in 1953. The owner, who was best buds with the drunks next door, was an infamous tightwad. It had some odd choices of light fixtures and a mismatched refrigerator and freezer, and a tiny "family room" added on, but nothing seemed to be wrong with it. Well, nothing you could see.
I had a large model train setup and huge slot car track (Thanks for the S&H green stamps, grandma!) set up in the back of the huge basement. About a month after we moved in, I was finishing setting up the trains, and I smelled plastic burning. I saw a little smoke coming out of the electrical box that powered my sisters bedroom which was almost all the entire second floor. I touched it and it was hot. So I opened it up and all the wire in it was brown, 16 gauge lamp cord. My dad came down and shook his head, and then called his dent headed (I mean a huge dent in his forehead!) electrician buddy who came (On Sunday!). He was muttering "Cheap BXXXard" and by dinnertime that night my sister's room had 3 10 gauge circuits running it. I helped pull the wires. That was in June. In October, we fired up the furnace and it caught on fire which I put out myself with the fire extinguisher she made my dad bring home.. Here comes "denty" again, and he opens up the furnace and all the info for the furnace, including the wiring diagram and the blueprints for the house were inside! He had to rewire almost everything inside the furnace. Funny thing, he used all blue wire for everything! This would come back and haunt us later on. Sadly, "Denty" fell though the roof of a local bowling alley and was killed. Just before my mom put the house on the market, the blower motor cooked itself and it caused a minor fire. We called a neighbor who owns a HVAC company and he sent a tech out who practically passed out with all the blue wire. He ended up rewiring it with multicolored wire. $$$
My dad never lived long enough to give the previous owner of our house a shot about the lamp cord and papers in the furnace, but I did. They had a party and for once, they invited us. Since my parents were just barely social drinkers they didn't fit in with them. My Beagle was outside doing his thing, which was yelling his head off, and the former owner, who was pretty drunk, says to everyone, "I wouldn't take that dog yapping, call the police, he's disturbing the peace of the neighborhood!". I was kind of waiting for him to say something stupid and off I went, "Well, at least he isn't the cheapskate who wired the top floor of his house with lamp cord, and put paper into the furnace, which started a fire! That was you!". Needless to say, he wasn't too fond of me from that point, or my dog, the biggest, toughest Beagle I've ever seen, almost 40 pounds of lungs and bad attitude
He came from a famous field champ who was the second biggest Beagle I've ever seen. Oddly, my dog, who was the runt of the litter and barely made it, turned out to be a clone of his sire, but even bigger. And even more likely to rumble with other male dogs. Man, he could yell.
When we moved into our 15 year old house in 1982 (Which passed an "inspection" with flying colors!) I soon had the "pleasure" of finding the following issues over the next couple of years. Some of these were just a total shock:
1. Every single pipe from the gas meter (Inside) to the furnace was barely tight. I found this after 2 gas leaks.
2. Almost every light switch and outlet had loose screws on the wire connections. Fixed all the lights that were flickering.
3. There was aluminum wire from the fusebox to the AC fusebox outside the house. Came home from a trip and it was about 100 degrees and no AC. Checked the breaker and found a bunch of melted plastic due to the wire arcing due to the clamp not having any tension due to the wire crushing under tension. An electrician friend came over and rigged up a temp fix as the breaker had puked. Turned out the company who made the breaker box went out of business in the early 70\s, and trying to find anything but a 15 amp breaker for it was not going to happen, so we put a new larger breaker box in and I had him wire me up a 6 outlet box on 2 20amp circuits for my hifi/TV set up.
4. Dogs started acting strangely, all three walked around with their noses in the air, sniffing. At first, I felt fine, but then got a mild headache. The furnace had a major CO leak and I had to shut it down. It was about 20 outside. Turned out the entire flue going from the furnace into the chimney was badly done. It was "fixed", but about a year to the day later, the dogs started their nose in the air thing and again, I had no heat. A new furnace resulted in a redone flue and a much better draft. Oh, and the original furnace had a pilot light that went out if certain doors and windows were opened at the same time.
5. And the biggest hassle of all of the issues, the gas pipe OUTSIDE the house was also loose and I came home one morning and before I turned into the driveway, I smelled gas. A call to the gas company, and the gas was shut off. It was 10 degrees out. The "recommended" contractor wanted $1500 to dig up the line. We checked with a friend who had a guy who would do it for less. He and his kids dug it up, and tightened up the connection. I ended up giving the kids an extra $100 each because it was such a miserable job.