I always make my requirements clear by text and confirm terms like OWO/CIM, DFK and RO (pussy licking) and get prices. Often I find an extra £20 above the stated price in the room gets me the service. Although recently, also in Sunbury an SP didn't like RO as she said it still made her come and lose control. She will almost certainly grow out of it. I wouldn't pay extra extra for RO but would for say CIM.