Size does matter!  At least when buying jewelry.  When buying jewelry on ebay (or online) the number #1 rule is to keep a ruler handy.  Why?  Because unlike jewelry you purchase in person an enlarged picture isn't going help you visulize the piece like you do when holding it in your hand.

You might think you know what a 2 1/2" brooch looks like, but if you keep a ruler handy you can have an instant reference to size.  A 2 1/2" object seems small, but it is a good sized brooch.  If you're interested in a piece, measure out the size in your hand to get a good perspective. 

For necklaces, know your neck size and how the various lengths hang on your neck.  Get your own jewelry box at home out and measure some of your necklaces so you know how a 16" or a 24"  (or any other size) necklace hangs on you. Remember 16" necklaces hang very close at the base of the neck.  Extentions are available so make use of them if a necklace seems too short. 

Earrings are generally very small in size and anything over 1" is a large earring.  Pictures on your screen are always enlarged to show the detail and this is especially true of earrings so be sure to know what size you are buying.  Again, the best thing is to keep a small ruler handy to visualize the earrings properly. 

Know your ring size.  If any doubt about this go to your local jewelers and be measured.  If you're looking for rings for fingers other than the traditional ring fingers be sure to have them sized also. 

Bangle bracelets are generally sized between 2 1/2" and 2 5/8" inside diameter.  This works for most people but is not universal.  This is slightly too large for some (myself included) and too small for others.  Other sizes are out there, but are more difficult to find.  If bangle size is important, be sure to double check the size of the inside diameter.  Many sellers will let you know how wide the bracelet is and most will tell you inside diameter but if the information is not there be sure to ask as buying a bracelet that is either too small or too big is going to be of no use to you.  Other bracelets usually have a length of somewhere between 7 1/4" and 8", though again there are exceptions.  Measure your own pieces at home that you like the fit and use that for reference.

If you get in the habit of measuring pieces for visual reference before buying you will ensure a better fit and buying experience online.