Haha. This happened to me just tonight! Just replaced an old freewheel and the new one is no good. 50 miles in and it's failed. When it went from "this doesn't feel or sound right" to "oh no I'm spinning" I was just a block from the LBS that replaced it. They had just closed of course but I caught the owner walking out the door as I arrived. He tried to oil it up. No dice. I'll be back in a day or two to get it replaced. I'm sure he would've done it then if I insisted but folks gotta eat dinner.