Some questions should definitely be asked others while they can be asked does not mean it should weight to heavily one your decision.
If you buy an hatchling this will be irrelevant, if you buy from someone (breeder) who know what they are doing, handling will be down to a minimum (such as maintenance), reason being a young BP under 200 grams should be handled to a minimum. When it comes to adults they do not have to be handled, this is a not a species that need to be worked with on a regular basis to make a great pet even if the animal was handled to a minimum.8. Has it been handled regularly?
Head and Tail? I am curious, why requesting a pic of head and tail in particular if you have a body shot.14. Could you provide a picture of it (Head, Belly, and Tail)?
Females on eggs yes it's pretty common however many people don't catch locks nor do they care to disturb their animals while breeding just to take a picture if they get lucky to catch a lock. If a male is a proven breeder it obviously means offsprings were sired. I have males that have sired offsprings and I never caught a lock.16. If selling as a proven breeder, can you provide a picture of the snake on viable eggs for female and locked for male (If applicable)?
If they are PH both parents will look normal, in other words pictures won't really matter.17. If selling as a Het or PH, can you provide pictures of the parents (If applicable)?
Personally I ask very little when buying from a breeder, I ask pic (body shot) of the animal purchased, weight, hatch date, prey type.
If I buy a proven breeder female I ask for the number of eggs laid in the last clutch, weight prior to breeding and current weight after laying (this gives be an idea on where the animal should be before breeding again.