Venmo is instantly reverisble much like credit debit. This is one of the most DANGEROUS ways to sell bitcoins and is favoured by scammers. We discourage using Venmo unless it is for very trusted trade partners.
Sent his venmo, and then decided to try to recover his btc by disputing. This is a brand new unverified user. Do not deal with this guy, he will try to get your money, then try to get his btc back also.