<< << Is it the reseller's fault? Case closed! >>
< Eh-n-n-n-n-nh !!!! > (Sound of game show buzzer).
I'm sorry, Ornery. That is the wrong answer. Under the Uniform Commercial Code and the laws of most (if not all) states in the U.S., there is what is called an implied warrantee of merchantability. It means that a seller automatically warrants that item must perform the function for which it is intended and promoted. It isn't a matter of "fault." It's a matter of legal liability. If the item does not work, the seller is responsible.
Since the price you actually pay includes shipping, the seller is responsible for completing his part of the deal -- delivering a working item for the stated price. These conditions may differ if the sales contract includes written terms specifying who is responsible for return shipping charges.
In the case where a customer RMA's a part that proves to be good, I think a service would be fair if the customer had not taken reasonable steps to verify that the part was bad. For example, in this case, it may not be unreasonable to try another CPU in the motherboard or to try the CPU in question in another mobo. >>
There's many loopholes to this, like time frame. In some states, for example, you only have, let's say, 7 days to "legally" stake your claim on the product being defective and needing replacement with a reseller unless posted otherwise. Typically, what is posted otherwise by the vendor's implied warranty is LONGER than what law requires. So discussing this above "law" is a moot point as it rarely applies to real life.