Sure you can. But as a business owner, there are many things you find more important, like the daily operations of your business over managing your own advertising! Because SEM takes a lot of time and effort to learn, it is better to work with SEM specialists to get your results. You can also hire an in-house marketer. But that person must know how to run effective SEM campaigns and be diversified in various skillsets under SEM. It is definitely cheaper to hire an outside advertising specialist or an agency, compared to an in-house marketer. 🙂