First of all, research about the company thoroughly. Check out whether it has a legal license to run the business. Along with this, collect information about past history of the company, about its team members and the outlook of the company towards search engine optimization. Review its past projects to understand the kind of knowledge it has for SEO and also find out its work principle. Also, you can know about the company from the customer reviews in its website. This will give you a clear idea about the performance and what kind of service the firm provides. If you are interested in the company's service, read these reviews thoroughly.
Next find out its approaches towards the search engine marketing. Once you find out the performance of the company, check what kind of services it is providing. As a rule, the company should follow a logical approach while doing the SEO. The logical steps may include researching the targeted industry, doing some online competition analysis and keyword analysis, selecting appropriate keywords, analyzing your competitor's marketing methods, and finally determining appropriate SEO strategies for your online business.
Check whether the SEO firm follows any black hat SEO strategies or not. Ideally it should follow only white hat strategies. Many online business owners avoid asking this question to the consultant firm. Because they think if they ask they might offend the SEO company. But as a client you can always want to know what kind of technique they are deploying. If you want to avoid any undesirable situation and want your site to rank higher in the search engines, do not hire a SEO consultant who practices black hat techniques. Also, if he firm uses automated submission, then avoid that company, because if you do automated submission, your website may be banned by the search engines.
And don't get carried away by the promises of the company you are hiring for SEO. They can tell you that they will get your website topmost position in few days. But that is not the truth. No SEO consultant can fetch you the top ranking because search engines do it at a random basis. Also pay attention to the time line they are promising. If they say it will take few days to rank higher in search result pages, do not hire them. Retain a company to do SEO for your website who promises realistic time line.
Next you have to decide whether you want to retain a very experienced company who is charging you higher, or you want go for a cheaper company but they do not have much experience. If you are confused with this, you can take a middle path. Hire a company who is charging you moderately and have established themselves as a good SEO consultant. And the company should be able to answer all your queries within few hours and will not take long to get back to you. Also, check if the firm providing any extra services such as key word research or on-page SEO. If you are paying more than average, you should get these extra services as well.