Quoted from Fatsquatch:Both of those apply to me, and I just can't imagine ever contacting a parts supplier and saying "Look, I know you sell your widget for $50 plus shipping on your website, but this other dude started selling that same widget for $20 less. If you can match or beat that price, I'll buy from you."
While it seems like your current supplier would bristle at that, it's more likely that he/she would appreciate it. There is a reason retailers do things like 110% price guaranty. They want to encourage people to bring lower prices to their attention. There are a lot of reasons why a price might be cheaper somewhere else.
It may be that the manufacturer dropped the price and your supplier doesn't know it yet. (Especially if they carry a lot of product) They'll be losing sales to competitors simply because they didn't know to update the price on their web site yet.
It could be that a Chinese competitor has produced a product and maybe it's lower quality. They'll now know that they should bring attention to the fact that their product is superior, made in USA, or whatever justifies the higher price.
In a lot of cases they'll call the manufacturer and say, "Hey, what gives? How's this other guy selling it cheaper" and it can result in the reseller getting an additional discount across the board.
The reseller would much rather know about a cheaper price someplace else rather than just sit and wonder why sales have dropped.
Saying this, I don't mean that some guy down the street is selling it 1% cheaper. I mean, if someone else has a similar or the same product for 30% less, and it's not a blowout or a sale or something, there are a lot of benefits for everyone involved if you call them and say, "Hey, look at this, what's going on here?"