Tigger -simply put, surveyors have nothing to do with reducing an asking price other than finding things in the home that are potential risks or potential costs to the buyer ie no felt on rooves, structurally unsound.
as a buyer you should seek a survey if you are not getting a mortgage - if you are getting a mortgage the mortgage company will organise a survey.
as a seller, you should expect at least a survey from the buyers mortgage company, or a survey privately instructed. Often buyers will use this survey to try and get the price down -sometimes its legitimate , such as if the surveyor finds something wrong ,sometimes its just an excuse and its up to you as the seller what to do in these circumstances.