“Should I hire a company to help me advertise my GSA Schedule?”
I would recommend you save some of your hard earned cash and take this on yourself. Post a link to your GSA Catalog on your corporate Web site; add same to your business card; create a blog entry that explains the products/services you offer; research which Federal agencies are spending the most on the product/service you offer and focus your marketing effort at that agency after determining where in that agency the buyers and decision-makers are located. In other words, focus your marketing effort. You might also search for potential teaming partners on the Schedule and improve your odds for sales. I hope this helps!