Quick, get an agency! Every day you don’t have one, you’re losing money.
An agency will almost certainly be helpful to you. Previous marketing efforts probably haven’t worked out the way you hoped. Outside assistance may help you increase your visibility and your profitability.
An agency could be helpful to you. You may have limited marketing resources, but you’ve got some things figured out. A long-term relationship with an agency will probably be beneficial, but you also might consider a shorter “mentorship” arrangement to help you get ready to handle things on your own.
You may not need an online marketing agency right now. There are aspects of your business which either make online marketing impractical and/or you have the resources to handle it on your own. Have a sit-down with an agency representative if you feel there are areas of your marketing you’re still unsure about.