It’s highly dependent on the person who stutters. It also depends on who they’re with and the circumstance. I’ve stuttered for 30 years and it really just depends for me. When I’m at my work or out in public I generally would like someone to wait for me to finish what I’m saying because it can be perceived that the person I’m talking to is annoyed I’m taking so long and doesn’t want to wait for me to get it out. But then when I’m with my loved ones who I know accept me and are patient with me, I let them know they can say the word if I’m struggling because when I’m in a comfortable setting it just helps me get my thoughts out faster and is more convenient. I would say just let the customer finish what he’s trying to say unless he expresses otherwise.