How I photograph snakes for sale depends on two things: (1) What snake are I am selling? (2) Who is my intended customer?
I look for different things depending on what I am buying. Looking to buy a het pied ball python....I want to see a belly shot of the markers. Looking to buy a scaleless head ball python....of course I want to see a headshot showing the scalation. Looking to buy a Toffeebelly hognose.....I want a belly shot.
Then you talk about customers. Look up some mountain kingsnake sale photos......that segment tends to use 'natural' type background such as granite or large rocks. Ball pythons tend to get photographed on white or black backgrounds. Selling to someone you don't know?....throw in a 'snake in the cage' photo to show that your enclosure is clean and the snake is kept appropriately. Varies depending on the customer.
There is no cookie cutter answer for your question. Mostly it is a judgement call and your customer's preference. I take a bunch of pictures and always leave it open to the customer for additional pictures upon request.
My main goal is always to accurately depict the snake you have for sale. This is in the best interest of yourself and the customer.