Don't wind up settling for jars in less than great condition. A jar, by it's very purpose, is destined to be shop-worn with chips, paint flaking and cracks. It just proves the jar was loved and used in its previous homes. But if you have the choice between buying great condition and less than great (at a reduced price), remember condition is what will sell later on and will increase the value of your collection.
This does not mean stay away completely from flawed jars, they do have a place in your collection. I have bought several jars that have a hairline crack or a chip, it depends on the jar, how bad I want it and how often I've seen it for sale. But I also know that chipped or flawed jar will be much harder to sell in the years to come.