Recently I took part in answering LinkedIn question “how to select righ web agency?”. I believe that information posted there would be useful both for people thinking about ordering web design and development and for web agencies who care about their business. I will quote my own advice, for rest you are welcome to visit link at the end of post.
– references from customers of that agency. It is important to hear what clients say;
– size. For some tasks and some clients smaller agencies may be better, while for others the bigger partners are preferred;
– delivery model. It is neither good or bad, but you often need to know, where your agency developers are situated. From one hand, if they are offshore, it may explain the lower price, suspicious otherwise. From the other hand, If your project may require on-site job, you will need an agency with local specialists.
Check this link for full Q&A