One of the most important considerations for anybody running an online business is search engine optimization. Without a good SEO program nobody is going to find your website. Many companies choose to outsource SEO, often because they don't know how to do it themselves. Even if they do know how to do it themselves it is a time consuming and tedious process that most companies would rather higher somebody else to do. If you are going to out source your SEO it is important that you hire a good company to do it, If it isn't done properly your business will fail.
The first factor you are going to want to consider when choosing an SEO company for your small business is their experience. You should ask any company that you are considering how long they have been in business and make sure that they have experience. You should also ask for the names of some of their other clients. One of the great things about the SEO business is that it is easy to determine how successful a company is at doing the job. Take the names on the list of clients they gave you and run a search on some keywords that would obviously apply to that business and see where they rank, if they aren't on the first page for any of the major keyword phrases you should probably consider a different SEO company. If a company won't provide you with a list of clients run a search on SEO related phrases and see where the SEO company you are considering is ranked, if they can't get their own site on the first page do you really want them doing SEO for your company.
Another important factor that you are going to want to consider is how they are planning to promote your companies website. Not all promotion methods are appropriate for all businesses and any company that has a one size fits all approach is not really working in the best interests of your business. It is also important to keep in mind that search engine algorithms change on a regular basis, you need to know that the company you hire has kept up with those changes. There are still plenty of SEO companies that are doing things that no longer work because they haven't kept pace with the changes in the search algorithms. In order to make this determination you are likely going to have to do some research so that you know what needs to be done to get your site ranked highly.
The last factor that you are going to want to consider when choosing an SEO Company for your small business is price. There can be a remarkable difference in price from one company to another. Although price is an important consideration it is not a good idea to make your decision based solely on this, a cheap company may not be able to do the job properly. SEO is one of those things on which you need to hire the best because even being mediocre is a waste of money. If an SEO company can't get you onto the first page of the search results they are useless.