I have a pair of slippers with Thinsulate thermal lining that I carry in my laptop bag.

If I need to take my shoes off then I put those on and keep my feet semi-protected  (from bashing my toes on chair legs etc.) and, since most houses I visit these days have wood or stone flooring, more importantly they keep my feet warm!

The soles are easy to wipe clean when needed, and whilst it also saves my clients from being exposed to my socks, it just looks more professional and caring.