Online marketing can be a great way to boost traffic to your website and therefore increase your enquiries and /or sales. Many companies already have a website but not all of them then market that website, and even less market their site in the correct way.
Some companies like to keep everything in house and therefor will employ a person or team to be responsible for the marketing of the company. Other businesses will task an employee with the job of updating the site and advertising it, even if they do not have much experience. This can be a dangerous idea, as not only can it cost you additional staff time and money but you could actually end up causing more damage to your online marketing than good.
I would always strongly advise a business to either employ highly qualified online marketing experts or to outsource their marketing to a specialist marketing company. A good marketing agency will pay for itself, meaning that you will make more in sales than the amount you pay them to advertise, although this may take a few weeks / months to start seeing the results.