http://revach.net/article.php?id=1082

Section: Halacha   Category: Tshuvos
5 Things To Look For When Buying Hadassim
  1. Mishulash - The main concern with hadassim is that the leaves should be in sets of three.  This requires examining that all the sets of three leaves in the required length grow parellel to each other. 
  2. Falling Leaves - Furthermore, one must check that no leaves have fallen off. 
  3. Dry or Broken - Also with hadassim, they must not be dryed out or broken at the tip of the branch. 
  4. Size - Preferrably, the leaves should each be smaller that a thumbnail
  5. Branch Exposure - Preferrably each set of leaves should be close enough to the next set that none of the wood of the branch is exposed.

Feel free to ask any questions you may have for Rabbi Moncharsh at www.revach.net/ask

Important Note:  It is important and customary that once you have your Arba Minim to show them to your Rav to make sure they are kosher.