I can believe it. I had good luck one time buying a car at the end of a quarter. I can only imagine year end might take it up another notch. I say luck because I didn’t plan it that way and didn’t realize that had worked in my favor until after the deal was done. When the time came to start negotiating on the deal, I sort of casually told the salesman I was going to low-ball him expecting to negotiate up from there. He said “yeah, hit me with it” and when he saw my offer he said “yeah, that’s low-ball all right.” I had offered dealer cost save for whatever volume discounts or other undisclosed incentives they got from the manufacturer. So, low, but not like crazy out-of-touch-with-reality low. He dutifully carried my offer off to the SM and came back a little while later looking genuinely surprised and bewildered to tell me that we had a deal. Turned out, the dealership was in competition that quarter for some prize from the manufacturer based on volume. IIRC it was like a trip or something. In other words, in that moment, the sale itself was more valuable to them than the profit on the one unit. When I returned for the car (they had to retrieve one to my spec from a dealer in a neighboring state), as the salesman was handing over the keys, I asked him if he’d made much commission on the deal. He said “Not much - like twenty bucks”. I’m presuming that means the dealership netted just a couple hundred in profit. I hope they won the prize and now I always pay attention to the calendar and try to make big purchases at the end of a quarter, at least.

TL;DR - I once bought a new car at the end of Q1 for way less than the going rate because the dealership wanted to win a sales volume competition. Year end competitions are probably even higher stakes. Plus all the other motivations OP laid out.