Ah, sales. The most "necessary evil" for job shop owners! I've worked with a lot of different industries and don't think there's any where they "hate" the customers more than a machine shop (definitely even more than fabrication). Okay, that's not answering your question. This part isn't either but, if you haven't, I would suggest ensuring that you have "maximized" your online presence. A good website developer can ensure that your SEO is operating at full potential and will maintain it for you. These days, that's pretty much "CODB" (cost of doing business). Next (sort of answering your question), is that you need to ensure there's untapped potential (i.e, if you hire a sales rep, they have the possibility of generating work for you). What's your specialty and does it need to change? Are you in aerospace and there's a lot of potential for extra work in hydraulics or some other market? If so, then you need to find the person who can properly "work" that market. They need to know your capabilities and have the ability to get into potential customers (something more difficult these days, given that everyone thinks they can find everything they need on the internet). You want a good hunter with a rifle that has a good scope and is hunting in an area that has good "game" than Elmer Fudd wandering around with a shotgun.
One resource you may want to look into is Manaonline.org. It's a trade association that bridges both companies looking for reps and vice versa. More oriented towards OEMs but still might be able to find someone through that source.
The Dude