Your job is to create artwork that your clients love and will pay for. If you lack the ability to create professional-looking artwork, I suggest you partner with a “starving artist.” These are folks that have amazing talent and will work at competitive rates.
I like to contact local colleges for help. Often, they will have a graphic art department. Tell them that you are looking for freelance help, but could work into a long-term relationship.
You can also find talented people on Etsy Studio and sites like Hungry JPEG. Find an artist whose style you like, contact them, and see if you can contract with them for custom work.
-David Gross, Condé