I will wade in here with a couple of "how big is your stash" stories.
I had a hobby store in Montreal back in the early 2000s, about fifteen years after I started my website. I have always been in the high-end scale model business, but this opportunity came up to move into an old Montreal scale-model landmark, and I jumped on it. I decided I would stock one side of the store with vintage kits and encourage clients to drop by to see the "new" collections I was bringing in from time to time.
Through my website, and the work I was doing on eBay, I was receiving calls on a regular basis to clean out peoples' homes, generally after an owner had passed away. One such story happened with a fellow from Boston. He called me and said he had a collection to sell, and would I drive down to Boston to pick it up. So, I zoomed down there with my old Chrysler van, paid $1200 for, I don't remember, maybe 600 kits and drove up to the border. I thought everything was on the level. I had documentation from the seller, a signed packing slip, and whatever else I thought the border agents might need. I was ready to pay the necessary taxes and get to the store.
Well, the nice folks at the border kept me there for four hours. They literally pulled out every single kit, and went through them, looking for, well, something. Finally, they asked me to explain, in detail, how I managed to score such a huge collection of kits, some of which they estimated were quite valuable, for just $1200. I had to go through the entire process with them, explaining how I come across collections on eBay, chat with the owners, slowly reel them in with a decent deal, and then make my way to an owner's house.
It turned out the two fellows were avid kit builders and collectors and they estimated the collection at thousands and thousands of dollars, not $1200. However, after my careful explanation, they took my card, said they would visit my store in Montreal, and wished me a nice day.
I made several other trips to New England in the next few months, and always made sure those two fellows were on duty when I got to the border.
In another story, a fellow here in Montreal called me to say he had 25,000 models to sell, and could I help him out. Well, that was something! His house was so full of kits you could barely walk around. Absolutely every surface was covered with multiple kits. One side of every step in the staircase to upstairs, and the staircase to the basement, were covered pretty well up to the ceiling. The problem with that collection was that he also collected cats, and he was a smoker. Well, I tried to sell a few of his kits on eBay but the poor fellow kept complaining that I could have gotten "two dollars more" for this or that kit. Because of the smell, I had to put a disclaimer on every sale, and I was not even able to bring them into the house to take pictures! I kept them in the garage and only brought home a couple of dozen at a time. I did not even want to bring them to my store, as the smell would have contaminated the entire place.
So, yup, there are some huge stashes out there!