In hindsight, I agree that the service is legit and usually reliable. I have no idea why I could not book a room online but instead had to call a toll-free phone number to use their service. I think this was an outlier and "something fishy" was definitely going on.
I'm using windows (10 or 11, it's old) and Spectrum is my ISP. The very first search result on Bing is Booking dot com. I went to the same Motel where we stayed and went through the motions of getting a room. In bold red letters is the FREE CANCELATION policy. The Booking dot com price is $52 per night more than we paid by calling the office directly. It is a small operation, not a big national chain.
No big deal, it's only money and we had a nice time.