Here is how I handled the problem.
I had Smart Pricing turned on. I had min price set to $68 and max price set to $200. This week, someone booked my place (instant booking with no discounts) for $55.50 per night. I thought, gee, I did something wrong. Again, last night, someone booked my place for $55.50 per night. I immediately checked every setting. I'm very well-versed with using the settings, and have never had a problem until this week (also, I'm a Super Host). I called Airbnb and they actually told me that Smart Pricing will ignore your min/max pricing settings. I immediately turned off Smart Pricing and went in and hand-priced each month; my location is very seasonal. Super Hosts are permitted to cancel any guest's booking within 24-hours for absolutely no reason at all. The next time my place books for less than my minimum, I am going to cancel the booking and send an explanation to the guest. My price is exceptionally economical. It's the absolutely lowest I can go. For me to book less than $68/night means I lose money (my cleaning lady charges me $50/cleaning, and I build that into the $68, so you can see what I mean.