My mother passed away last year and I handled the home sale as I was the executor of the estate. The buyer was a neighbor who heard about my mother passing away and saw it as an opportunity to buy the house for so his mother could live less than 100 meters from him and help him and his wife with raising their kids.
He knew we'd be eager to sell and thought he'd get a deal, but I realized that the reason for him wanting my mother's house was because it was ideal for his particular circumstance. This buyer was a real estate agent in my mom's office (she was also a real estate agent). At the end of the day, I got about $40k premium over the appraised value (almost ~10% premium) just because I knew I had a motivated buyer.
Situations with motivated buyers and sellers happen all the time and adds a lot of volatility in sale prices, and is a confounding factor that I would expect to really complicate machine learning approaches to appraising the value of a home.