Building society guy doesn't know what he's talking about (and should be glad your son is prepared to pay for a full survey - less of a risk for them). Full surveys are usually done on old houses, especially if you are concerned that they may have dodgy rooves, bulging walls, subsidence, supporting walls that have been removed, plumbing, electrics, sewers etc. If your son has concerns he should get a full survey - a basic survey only basically confirms the value of the house and that it actually exists. Obviously, if the house is new, then a basic survey is all that is needed.