I hardly ever get revisions, and I don’t have any options on it. I just do 'em as the changes are usually only going to take 5-10 minutes (as a writer–I realize that with graphic design, VOs and other areas it’s not quite as simple!). Some buyers will just abuse the button, even if it’s just to share their thoughts. Those annoy me. Just… say something then review me or go away, or inbox me.
Actually, I lied, my sucky website gig has a no revisions option and of course people ask for a revision. It’s like… dude, this is an opinion gig. You want me to revise my opinion when you’ve ordered a gig to see if I think your website sucks? lulz.
Anyway, just either charge for revisions, or set a limited amount of revisions and note that extra beyond that will cost $x per y revisions. Or just do them anyway. If they are obviously abusing the feature, then contact Customer Support–they will be on your side if you can prove that you have done the job to your gig description (minimum) and especially if you deliver a little more to appease them. You don’t need to bend over backwards for the unreasonable buyers–just get off your knees