First let me say I'm not happy with buy.com's pricematching as I got scr*wed about $30 (roundtrip shipping charges)last time I tried it.
Second, they do indeed pricematch more vendors than those listed in UnAshamed1's posting.
Third, unfortunately, you can't tell what they'll do with the pricematch until it's too late to cancel, in which case you can lump it or ship it back for a refund THAT DOES NOT INCLUDE THE INITIAL DELIVERY COST OR THE RETURN DELIVERY COST. (!@#$%^& !@#$^%^&*(!!!)
A while ago someone posted a deal on a Nikon camera with a mfgr's $150 rebate and suggested a pricematch to a site that, on purpose or by accident, had a sale price net of the rebate that actually appeared on your checkout page "net of mfgr's rebate."
It was a great deal, but, being a greedy little duck, I went to buy.com, applied a $30 coupon for a returning customer purchasing over $150, and bought the camera AND applied for a pricematch using their electronic system, which is the only way you can pricematch.
They subsequently "determined" that the PM$ was net of rebate and added it back and sold me the buy.com price less PM plus rebate less $30 plus shipping, and the shipment was on the way. I was NOT given the opportunity to turn down the inferior PM they substituted. Well, in the course of things it became pretty easy to get the camera at about my first PM price, but I was stuck with buy.com's !@#$% return policy and PM procedure.
I thought about calling up and making a scene, but decided to just avoid them, unless their deal is rediculously below everyone else's.
In any case my lesson learned was "DON'T PM buy.com!!"