Whether or not to reuse bedikah cloths is a matter of personal preference. As long as you are careful to make sure there are no stains left on the cloths after washing, reusing bedikah cloths would be acceptable. Those that are significantly stained may be more difficult to get perfectly white and are probably best thrown out to prevent confusion with future bedikot.

You should make sure to examine used cloths carefully right before you use it. In fact, all bedikah cloths, even new ones, should be checked prior to use.