In order to quote shipping costs on your ebay listings that are fair to both you and your buyer, you have to be able to weigh the packages, especially the heavy ones.  Regular postage scales can be expensive, bathroom scales can be inaccurate and they are hard to read when you have to balance a  bigger box on the small base.

I have discovered that a digital fish scale like the kind sold in the hunting and fishing isle of most  department stores solves all these problems; they run around $15.00 for most major brands and run on AA batteries.  Simply hang the fish scale from a hook at a comfortable height to see the display, use a bungee cord or strap around the box and hang it on the fish scale from the hook the fish should be on.  Be sure to subtract the weight of your cord or strap and you have accurate weight up to 50 lbs.  It is the best way I have found so far to weigh my ebay boxes.