You should at the very least take a Master Gardener Course from your state's extension service. Most people have no idea what is involved in 'Landscape Design'...nor maintenance. Thus you will find yourself if you've no education grouped with all those making money using a pickup and mower.
The more education you get under your belt, the more humble yet effective you will become. Landscape Design is far more complicated than drawing pictures and planting plants. Far, far more knowledge is required!! Get educated if you want to be good at Landscape Design. Sure, take seminars...you have to get to a point that you are able to recognize what is a great design which will be inherently low-maintenance and what are 'old wive's tales' or just bogus ideas promoted to sell a product.
Another suggestion would be to take a pesticide applicator course from your extension service. Doesn't mean you will learn about the chemicals...you will learn how NOT to have to use chemicals. Quite an eye-opener! They make sure you know the difference between plant biology and animal. Basics you HAVE to know and understand. Go back to school!! You will see what I mean once you get proper certifications. Then you will be able to compete in this industry. Otherwise, you like an awful lot of others, are just taking advantage of ignorant customers.