Just ask the owner how she feels about your giving her horse a kiss. What is the worse she can say no.
I kiss my three, but don't kiss other people's horse.
You just never know if there is something hidden on their muzzles/face. A friend many years ago kissed a friends horse who happened to have gotten into poison ivy. Yup her lips swelled right up. You just never know.
Two of my girls will kiss/rub my cheek after I give them a treat. Never trained them to do that they just do. Like saying thank you.
My old gelding used to whinny and run to give me kisses when he saw me. He was a funny boy. He wouldn't give me a kiss on cheek right on the lips and he would pucker his lips it was the funniest thing. I miss my old boy he one of those one in a million horses.
My Percheron is not at all into nose kisses, but he puts up with me. I figure he has little enough stress on him during the day.. what does his schedule look like? Eat, sleep, eat, walk around, eat, chuck a buck at a passing snowflake... so if I want to kiss him, he just has to suffer it. What he really likes is scratches down the sides of his windpipe. He just about falls over in ecstasy.