Why do you worry about the guest's interest is not high. Why are you worried that their interest is not high? What you will find them on the brand, or to buy the car of interest as you imagine so high.
Why are you worried that your guests are not interested. Why are you worried that they are not interested? Where do you think they're not as interested in the brand, or about buying this car as you might think?
Why do you worry about the low interest of the guests. Why do you worry about their low interest? In what ways do you think they are less interested in the brand, or in buying the car than you think.