For residential customers, get a deposit that will cover your cost of material. Buy at wholesale, sell at retail, put money in your pocket instead of a retailer's pocket. Since you are new to landscaping, find re-wholesalers such as Shemins that sell only to the trade yet let you buy small quantities and sometimes even provide a warranty. The warranty is the biggest issue when buying wholesale, which is another reason to mark up plant material in case you have to replace it. The other point that I see is when you spend your money for materials you are making an investment and should expect to see a positive return on that investment. Otherwise why 'risk' the money?