If you are trying to start business where human interaction is important thing, you should get used to people disagreeing with you. Also you should try to learn from other people thinking and advices (not all of them are useful, but some are). Customers will always try to find negative things first, only later on will they look for good ones. But that should not discourage you, also you should not give in to your negative attitude, because that will force away your potential customers. This example shows that you still have much to learn about social relations, but keep the hard work and one day it will pay out if you do it right.