I am mildly obsessed with Jigsaw Puzzles. If I could, I would spend my entire life solving them. I especially like the 3-D variety. They require a little more brain power than 2-D puzzles and take up more space once completed, so naturally, they are not as popular. I've found that people will buy them, realize they are not what they expected, and then give them to Salvation Army or sell them at their garage sale. Then, I come along and buy them for two dollars. There might be missing pieces, but with two dollars, you get what you pay for.
I once bought a 3-D puzzle of Notre Dame Cathedral using this cheap and effective method. As I was nearing the end and it was almost completed, I determined that I was missing four or five pieces. Fortunately, there were diagrams of the structure and all the included pieces. On it, it said if there were any missing pieces, to clearly indicate which pieces were missing on the diagram and send it to the company and they would send the missing pieces free of charge. I took great care and put a lot of effort into indicating which pieces were missing and promptly sent off the envelope to Hasbro Games. About a week or two later, I received a curiously flat envelope for Hasbro. They thanked me for my interest in their product but were sorry to say that the puzzle I had had been discontinued.
My puzzle sat on my shelf above my desk for years, holes and all.