Look here:
MANAonline.org
MANA is an organization of professional Independent Multi Line Manufacturer's Reps. I am one, but in a different business as machine tools are only my hobby.
One of the advantages of a good rep is that you have no fixed cost of sales like you would with an inside sales staff. Your costs are a percentage of sales (commission)so if business is slow, your cost of sales goes down. On the other side of the equation, if business is booming be ready to write some big commission checks, but don't wince too hard because business probably wouldn't be booming without your rep network! One of the things you buy when you engage a rep firm is access to a whole bunch of accounts that you either would never find, or would take you years to develop a relationship with. The rep probably sells them a couple different lines of products and has these relationships in place already, they're his stock and trade.
MANA consists of reps in many industries, from industrial stuff like screw machine products, to guys like me in the home theater business. Their site has a lot of information pertaining to some of the stuff Ferrous mentioned above like determining sales territories, commission rates, etc. Hope it helps.