More detail on pre-purchase check - fridge,water heater,etc?

When I sold a TT a few years ago in mid winter there were a couple of systems the buyer was unable to check. I told him that everything worked when I winterized it but I gave him a written guarantee everything worked that was for 72 hours so he could get the unit home and check everything himself. Turns out that a circuit board in the furnace failed during storage. I told him to get it fixed and send me the bill. He was so impressed he said he would pay half of the bill. Everybody was happy!