How often should an editor ask for reviews from the same referee?
From my experience as an editor, it is not unusual for referees to ask for &quot;time off&quot; from being assigned reviews and give bounds for the frequency of requests.  As Buffy suggested, some editorial systems allow referees to enter this information and the editor sees it before sending out review invitations.  I was glad to honor such requests from reviewers---I wanted them to feel satisfied &amp; respected so that they would write more helpful reports in the future.
Similar to Fred Douglis, I tried not to ask anyone (other than editorial board members!) to review more than twice a year.  However, we aren't mind readers.  If your pattern is to submit a helpful report and then say yes to another request soon afterwards, then maybe you have the time, really enjoy reviewing, etc.  What editor wouldn't follow up on such enthusiasm?  My advice is that it's up to you to speak up about what you have time for, how often you're comfortable reviewing, etc.  I think there's very little risk of getting on the editor's bad side by setting up those kind of parameters.