Supppose you send him one more message and he doesn't answer. You sell the snake. Then a week goes by and he contacts you and says something like 'there was a family emergency and I was out of pocket. I'm now ready to complete the transaction'? You've sold the snake and kept the deposit!

Since you did not specify how long the transaction was allowed to progress, I would not sell the snake unless there is clear confirmation from the buyer that he has backed out. Silence could be for many reasons.

If you accept deposits, you should state clearly and in writing that the deposit will hold the animal for a specific period of time. Without that, it is an open ended transaction with no end date. I'd continue to try to contact the buyer and confirm they have backed out. Then you can decide what to do with the deposit.

Some people will refund the deposit once the snake sales to someone else for the same price. Others will keep it to pay for the aggrivation, feeding and care during the waiting period.