I would pay more from a breeder who microchipped their snakes, and with the chip number for the snake tested being included in the paperwork.
What I don't see is breeders going that far to reassure buyers.
That said, if I wanted a boa tomorrow, I would ask the breeder if they would be willing to take the chip, get it microchipped and tested for me, at my expense (non-refundable regardless of outcome of the test and including some extra cash for their time). *That* might be something I could convince them to do.
It would be a heck of an expensive proposition, but it's also about the only way I'd bring a boa in.