Three simple things which shouldn't be difficult for people working in a service industry providing something to a customer:

1. Reply to emails within 24-48 hours, even if it's just "I'm still looking in to this for you - will update you when I hear more" (my holiday is important to me, therefore it should be important to you, even if it isn't earning you $k's of commission)
2. Just tell me if it is just as easy to book myself or if there is no benefit to be gained by booking through you (especially as I'm the type to do most of my own research)
3. Don't get sassy with me if my plans change and I need to cancel / look at an alternative

Generally have had excellent experiences.