Facebook has been used for a number of years now by companies as part of their marketing strategy. Some businesses do not like the idea of using some social media sites such as Facebook as they feel it is not professional enough, but in doing this they may be missing out on a potentially huge amount of business.
More and more people are using social media to find products and services they need, even professional services such as accountants and architects. For this reason it is vitally important to have a presence on there. It may be that you do not get any enquiries directly through the social media sites, but it can all help to build up brand awareness and trust. You may just use Facebook as another form of contact for some people, as if someone can quickly send you a message they are more likely to contact you than having to pick up a phone. This can make it easier for people to get in touch and again act as a plus for your business going forwards.
IF you are unsure of how to go about using social media then you may want to go on a training course or outsource your social media to a third party to manage.