This is nothing new but as traveliz said if you confirm then you lose your one allowed reschedule. You'll also notice all of your shops say "assigned". If you confirm it changes to "confirmed", if you've ever rescheduled a shop you'll also notice that when you make the new date marketforce considers that to be confirmed too. Marketforce's shopper grades are entirely secret to the shopper but I know they have one. I'm almost certain if you cancel a "confirmed" shop that, that hurts your shopper grade more then if you cancel an "assigned" shop too. I can't say for sure but I have a pretty big feeling