Your first impression about the company is essential for good choice. Simply visit their site and take a look at it as a designer. Do you like its external look, its concept? is it clear for you? If the company can't represent itself properly, it's most likely that it won’t be able to represent you. Actually, the web site is one of the most valuable sources of information, you just need to know what information you are looking for.
First of all take a look at a portfolio, just the presence of it on the site is a big plus for the company. It represents openness and, of course, it is a demonstration of its skills and abilities. A good team page and a variety of contact options on the contact page also shows transparency and reliability to the customer.
Another thing that definitely verifies the professionalism of your potential contractor is certificates and awards. Just make sure that they are given by prestigious organizations and companies in this field. And that’s pretty much it, what you can take from the site.
Then it is time to dig deeper, it is time to look through the forums and feedback from previous or current clients of your potential contractor. This is the most reliable way to see the real face of the company. However, just like awards and certificates these forums and communities must be well known and prestigious, these communities usually have restrictions on the evaluations and comments. For example, the biggest freelancers exchange Odesk has restrictions on commenting, only real clients who have worked with the company can leave feedback and comments.
The other place where you can find needed information for your choice is social media. The way the company treats their community in social media profiles can show you company’s attitude to its customers, and what is even more important to your customers. A good contractor in ecommerce knows that their success depends directly on his client's success on online market. And if contractor is aware about that, and company’s aim is a longterm business relationships, they will do their best.
And the last thing that you need to pay attention is narrow specialisation. Highly specialized companies submerge the whole team into one single theme. Efficiency of these teams can be higher than generalize rather than having a key specialization. The only problem - such companies are very, very rare.
What criteria do you use when choosing your contractor?