Here's some pointers for people new to sales or purchasing.
1) If you walk into the front door, asking about what used vehicles we might have for sale, and you portray yourself as being in that line of work, maybe you should know things like 'blown head gasket' + 'no compression' = 'not driveable' instead of asking the same question three times. Correspondingly, whatever it is that you sell, try to learn your product, and not get schooled on it by the person you're trying to sell to.
2) If you walk in the front door asking about one thing, and then feeling like you can't get what you want from that, start asking about seven other unrelated things, be prepared to be treated like a) an idiot b) a miscreant or c) both. If you don't like the vehicle we might be able to sell you, and you start asking about pallets and breakers and scrap wire - I might think that you're a junk dealer instead of a vehicle broker. If you pursue the issue further, I might think you're just a criminal casing the place instead of a junk dealer.
3) If you want people to think you're sincere, dress the part. I'm not saying business suits and ties are mandatory, because I wouldn't wish that on other people. A shirt with a collar goes a long way towards sincerety. A business card with real contact information wouldn't hurt, either.
4) Be straightforward. Saying you're in "the export business" in a vague manner may sound impressive to the guys at the bar, but it sounds like "I'm trying to be a tax dodger" to someone with some accounting knowledge.
5) Drive a sensible car to a business call. If you roll up in a luxury SUV with gold trim and fancy wheels it says "I milk everyone for so much money that I can drive an empty land yacht and don't care about gas mileage."
In the interest of disclosure - this is basically me ranting about someone who showed up where I work and proceeded to waste my time. I don't know if he really was a broker, or he was just a hoodlum, but now I don't care and will be letting less of them rob any time from me at all.
If we sell anything used direct to the public, we'll use craigslist like everybody else.