Sample sales are usually with clothing, shoes and accessories. They are when a designer makes one or two of a particular item and sells them at a deeply discounted price because they were the 'firsts' that were made. They usually do not have blemishes or anything of the sort, they were just made and the creator decides that they want to change the design a bit or improve on something. That is the case with me. Sometimes I'll make something and decide that I want it a little bigger or smaller, to add or take out a snap or to add more interfacing in some places. That's what happened with the July Day Bag and the Dorota Bag.
Clearance is when something has been around a little bit in a shop or a whole new style of that item came out and the designer wants to get rid of it quickly to make room for the new version. It's not that it's bad, just that a pocket that may have trademarked an item was moved and now it is the new style of the season like my Jane All Day Tote.
My advice is if you see Sample Sale or Clearance anywhere, go shop there first! You could find exactly what you are looking for at great prices!