I've always offered this at discretion, and make it clear in my advert that it will be my choice whether we kiss or not! Lots of reasons as to why I won't kiss someone, the main one being poor personal hygiene.
It hasn't affected business as far as I can tell, as there are quite a few clients who prefer not to kiss SWs, and also a fair few who prefer not to have full penetration.
There's always something out there for everyone, and you will get clients who specifically book you because you don't explicitly offer "full service". Some clients just want a cuddle and a chat, and maybe a happy ending.