Never, never, never.
I feel sorry for vendors. They're so easy to take advantage of. Let's take a look at a perfect example - my CDW rep.
He provides products, services and one-on-one attention. He helps me do my job by getting me what I need when I need it. He's nice, prompt, funny and occasionally answers the phone. He's a pretty normal guy - a loving father of three who works from home on Fridays so he can see the kids he's trying to feed.
Why would you want to hurt this hard-working family man?
Because it's fun, that's why!
It starts off small, like asking for a price break or free shipping on larger orders. If this works, then you know you have a patsy. Patsies are the pushovers you need as part of your ordering process.
Patsies make talking on the phone worth the time and effort:
Me: I'd like to order 10 laptops, please.
Vendor: Sure thing, Mr. Anderson! Anything else I can fall over myself to get for you?
Me: Well, since I'm ordering in bulk, can you knock $50 off each one?
Vendor: Ouch! Sure thing!
Me: *Confidence growing* Oh, and would you throw in 6 flash drives and a couple dozen optical mice?
Vendor: You drive a hard bargain! Will that be all?
Me: *Confidence enlargement complete* Sure thing, Pat. Do you have any swag? I could do with a CDW hat and maybe a couple shirts.
Me: I'll take the large - thanks!
Vendors are people, too. Don't take advantage of them. Be nice.
Remember, it shouldn't hurt to be a vendor.