For $400 he not only needs to supply a picture, but age, health, shedding, feeding and any other records including information about where he obtained the snake. He should expect any serious buyer at this price to ask for these. Otherwise it is a $40 snake. The fact that you are supposed to accept his price before getting answers to questions, and that further information depends on a making commitment to buy sight unseen is very suspicious.
When you are trying to sell something it takes work and giving information including pics to potential buyers is part of the process. If he's this lazy I'm suspicious of his care of the snake.