Regretting buying?
Oh, yes.
On the bushcrafty/ethnic side, I was offered to buy a small collection of Sámi stuff, knives, boots, items of clothing, outside implements.
I wanted to only buy the knives, but the seller wanted to sell as one lot.
Then, in the good old Iron Border times, I passed on a Patek Philippe pocket watch with complications, as I only collected wrist watches.
I could have had it for the value of the gold case.
Big regret there, wife and me still talk about it.
Then in the weeks after the Velvet Revolution, I had the possibility to buy cars from before WW2. Private small collection, old guy. Unrestored, but driveable. Fully complete.
Dirt cheap.
He even offered me three cars in exchange for my Nissan Sunny GTI.
I regret not swapping and getting a BMW 328 and a Tatra 77 too.....
The worst is, the Nissan was a real pos. Brand new, had lots of issues, including paint that came off when you washed it.