Here are 5 things to remember while choosing a reliable web design
Selection of the agencies
Meet up, share yours & get theirs
Checking out the work
There’s a difference between a suggestion & interference
The list of the requirement
The agency wants your list of requirement, so be ready with the list. If something got missed, it can mislead the project. As per your requirement, the agency suggests you the options that is best for you and suits your idea.
Getting ready with your requirements and these things will help you out to choose reliable web design services and choose the agency that is right for you. This is kinda homework which as a client should be ready with.