Ask Bertie, didn't he do something similar a few years ago?
On a more serious note, see what similar houses in the neighbourhood are making and go with that; you will save on fees but don't have the risk of going to auction. If you do put it on the open market, you will probably have to do vacant possession.
Also, the tenant may have an unrealistic expectation of what he can buy the house for; have you asked him/her what they are willing to pay for the property? If it is way too low, probably no point in discussing it much further with them.