I should have noted my experience is in the automotive business.
48th just gave you probably the best run down anyone could. I do partially agree with gks452 as well, but if you're smart about it you probably won't end up getting sued.
However, we started off easy by just ordering from a wholesaler. As we sold more and more parts, we ended up jumping from wholesaler to wholesaler based on our parts sales and the requirements to get into their programs.
Usually you can buy into a whole mess of companies products through a wholesaler for the same price of the buy in for one particular company direct. The cheaper the wholesaler sells for, the more parts you typically have to order per year. Now we buy about 40% of our parts direct and the rest from a wholesaler. We're very careful about it as the wholesaler can get alot of parts cheaper then we could get them direct even after the buy in.
Getting to know the people you're buying from is a good idea to. If you can't have a good conversation with the guy who handles orders at the place you buy from, chances are you're not going to move up as fast (meaning better pricing, treatment, and such). It is about the money, but having friends in the industry doesn't hurt.
Don't try to compete with other vendors, just be as honest as possible and help people out as much as you can. Also remember that if a person has a good dealing with you, he probably only tells two people. If he has a bad dealing with you, he's going to tell everyone he can. You also get to know alot of people through the business. As I said earlier, if you have repeat customers get to know them. If you aren't a people person, you shouldn't be in the business.
I know this probably sounds super cheesy, but alot of customers aren't really customers at all. They're just friends that buy stuff from you.