Those are great questions: Since it's not your first reptile or snake, you shouldn't worry about getting a young BP...if anything, they're more resilient,
whereas an older snake may have some pretty firm feeding preferences or be more stressed by re-homing. Since you've expressed awareness that "baby"
snakes might need some TLC, I suspect that your "instincts" will guide you pretty well, and it's really awesome to watch a snake grow up under your care.
If the price seems too low, that can be a "red flag"...or maybe for other reasons, that seller is motivated to downsize the number of animals they have to
care for. This is a time where you should try to research that seller's reputation...maybe ask on Fauna Classifieds too. Prices can be very subjective- males
can be cheaper than females (since many people want the option of breeding their snakes). Does the seller offer any sort of health guarantee? Can they be
reached locally...or are they only known by a P.O. box? Can they offer any references? Ask questions...is the snake feeding & on what? (live or f/t, mice or
rats & what size?) Listen to the snake's breathing (you don't want to hear crackling or whistling)...are the tongue tips stuck together? does the tongue-flicking
seem normal? any wounds? signs of diarrhea? stuck shed or eye caps? etc.