You are going below the price you think you need to make a living. However it is not below the price you actually paid for the item.The plus is you AND NOT SOMEONE ELSE sold this person the device.
I know some have the mental block about "if I sell this to him I have to sell it to everyone at the same price". No you don't .
I guess if you have no talent at reading people, this will not work, since you cannot really know who is going to go buy it someplace else. But if they say to you.. Haggling.. I can buy this at Joe's Junkyard for $xxxx. And you say goodbye.. You are not a smart businessman.