You can be having a great day, then you stub your toe. Now the day is not as good.
But it’s not just a physical experience that will influence your emotion. It can be someone flipping you the bird, or someone giving you a bouquet of flowers. Someone smiling or scowling at you will shift your emotions too.
You absolutely have influence over your client’s and prospect’s emotions.
Deliver your service with a smile. Answer the phone with a cheery voice. Thank your client and occasionally give them a small gift. All these outside influences will make them happier. And happier clients are good for business.