That is right. Since you know the person so well from your previous job, you can judge if they are fit for the position or not. If they were so incompetent when they were your boss, you wouldn't think of hiring them.Yes if he or she will be capable of doing his or her duties very well. Though it all depends on the individual and how you see them, there are some that will not be able because there only think of the pain or stress he put them through.