client: that cordless mouse you sold me is broken.
me: ok, no problem, i'll comeover and double check for you and if it's defective, I'll be more than happy to replace it with a new one or refund your money, but if this isn't a problem with the mouse I am going to have to bill you for a service call-$40.
client: Young man, I know how to use a mouse and I'm sure that this it is defective, the IR is plugged into the USB port and I just replaced the batteries so I'm sure it is defective and I would appreciate it if you would just refund my money.
me: OK, I'll be right over to rectify this for you.
Upon arriving at her house, I check it out and sure enough the mouse is not moving the cursor. I open the battery case on the bottom of the mouse flip the batteries around, put the cover back on-VOILA cursor moves.
me: That will be $40 dollars, please.