Selling travel is much the same. With so much experience in the industry, there is knowledge and confidence that you have, but the average traveler does not. If you have a client who seems exceedingly picky and asks you about every little detail of a trip, it is because they want to know what to expect. If your client seems to be really worried about making a connecting flight or meeting up with their hotel transfer, it is because they have may not have done it before. They trust you to book them the perfect trip, and your assurances and enthusiasm will go a long way.
With clients who are frequent travelers, and especially with those who are not, making sure that everyone is clear on all the details and reassuring them that you have everything under control will allow them to stop worrying, and to get excited about their journey. After all, it is a once-in-a-lifetime event - for them.