I tend to agree that a lot has to do with breeding, how much the breeder handles/works with the snake, and individual animal temperament.
I have two BI's from a breeder who is small and works with his animals and knows their temperaments inside and out. Both are docile as can be.
I also have a dwarf Venezuelan BC from Tommy Carpenter, of TC reptiles, and loves these guys because they are so docile. Feliz was no exception and he was a holdback and Tommy had spent time with him. He had two holdbacks in 2018 (from his 2017 litter) and I talked him into selling me Feliz.
I would tell you that babies can be nippy and scared, but Boas tend to grow out of that pretty quick and know their size when they get bigger. Since snakes bite out of fear or hunger, a snake that knows you really cannot hurt it is generally a docile snake. Boas fit that bill and most are puppy dogs at size and even much before they reach adulthood.
My recommendation is to speak with different breeders of locale boas, like Tommy, and feel them out. See what adults they have of certain locales that are particularly calm and ask about the offspring. In general how they are and specifically if they have any animals that stand out as both good eaters and docile.
Remember, a healthy boa has a voracious food response, and I recommend hook training all boas. However, once out (and hook trained) boas tend to be incredibly calm and docile while also being inquisitive.