Customer satisfaction should be the main priority of any company. If they cannot satisfy you with their services you should not give them a go. So, have a meeting with the company’s representatives, discuss all the points you have in your mind, tell them what your expectations are.
You can ask them different questions like how many years the company is working. What is the method they use?, or you can ask about the chemicals they will use, are they less toxic, What will be the effect of those chemicals on the environment?. If they can stand on your expectations you can choose them.