I have approached a domain owner about purchasing their domain. We have agreed on a price, what is the safest/best way to send them payment and ensure I receive the domain? 
How to avoid fraud when purchasing a domain
domains;domain registration;purchase
There are some website that offer escrow services: https://www.escrow.com/http://www.sedo.com/us/services/domain-escrow/Selling/buying a domain is safe that way.You can also do a down-payment (lets say 50%), the owner transfers the domain, and you pay the other 50%. The latter is more about trust.