I was reading through the comments on the FreshTECH Electric Canner a moment ago and saw several people mentioning their frustration with their current canners because they left spots and rough deposits on the jars. Happily, there is a way to prevent this without investing in a new canner. Pour about 1/2 cup white vinegar into your canning pot when you first set it up.
Whether the residue on the jars is minerals from hard water or particulate matter from your canning rack, adding vinegar to the water will help keep it off the jars and prevent build-up on the inside of your canner. Make it part of your canning routine this summer!