Personally I wouldn't chance it. I wouldn't do it, if it were one of my vehicles unless it's someone I know, or someone I can contact easily.
Discharging liability- That's the biggest thing you must consider, your liable for that vehicle until the DVLA are instructed it is no longer in your posession. If someone comes to pick it up on a truck and the actual purchaser isn't present how can you be sure he sognes the V5C and it is completed properly. The driver isn't going to sign the V5C, you must cover yourself at all times.
Any vehicle I sell comes with a bill of sale, with date/time of transaction and many other details. Both myself and the purchaser sign so I can discharge my liability. If the vehicle was used for illegal activity it would still be registered in your name, but a bill of sale that clearly shows, when, where and to whom the vehicle was released would be enough to cover you.