Apparently staff are watching and will manually cut you of if you go over, so you got thanked because they didn't have to force it off for you.Its not like they can enforce it. I called in at one last night with a £30 limit and put £30.01 in and the lady behind the counter thanked me as I was the first person in the last hour to stick to the £30 limit. Its not like they arent going to take your money from you after you have put in £80 are they? Especially if its not your local./regular fuel station, its all done on trust that you wont go over the limit.