If you are going to sell items online a shipping scale is probably the most essential tool you will need. It really is almost impossible to be in this business without a scale. Without knowing the weight of an item you will either be stuck with only using flat rate mailing boxes and envelopes or having to guess and hope you are right when you go to the Post Office to pay for the shipping.
Not all shipping scales are created equal. They have different weight limits, different weight increments and various other features which you may find extremely valuable or completely useless. One feature you will need is a scale that displays not only pounds but also ounces. I have a large shipping scale that goes upto 150 pounds but does not give me the ounces of an item. This scale is great for large packages however it cannot be my only scale because to ship anything via First Class Mail I need to know the ounces that the item weighs. Another feature that is really handy is a remote display. This simply means the screen that displays the weight is not directly attached to the scale. The screen will be attached with a wire (usually a phone cord) and can be placed anywhere. The first time you try to ship a large box you will know why this is a very nice feature to have. Many of the other bells and whistles a scale may come with I would mostly consider fluff.
Below is a video I posted a while back regarding shipping scales: