My yard is small. You should interview no more than 3 contractors,generally. Check with the Better Business Bureau in your area. See if they are in good standing. Check with the local licensing authority in your state for license violations or actions.
Many companies employ salespeople to meet with prospective clients.
They usually sell the pool and options, explain the process of the construction,and sign the agreement with you. You should be comfortable with the answers to all your questions and sure of what you are getting. Some other companies are smaller and the owner may see you in the estimating process. This can be a good thing for you as he is going to be involved in the day to day construction of your pool. You usually only have to make one call to get in touch with the person in charge, and this can minimize confusion over what is to be done and any changes by you can be addressed directly.