Rich people leave tracks and it's easy to locate them. Sell at a high margin. Use preferred suppliers. Choose your customers well. Remember, one of the greatest advantages the home-based travel agent has over the traditional storefront agency is that you can define your business any way you want.
Experience shows that specialists earn more than generalists.
The increased knowledge gained by focusing pays off big. Track your commissions. You'd be surprised how much money goes missing because agents don't do a good job of keeping track of what's owed them and making sure they get it. Always ask for more. Better commissions, better terms, better perks.