They're saying that if you time it right, they won't get/hear the notification that you've checked in and you can slide into the right spot. Wait awhile and then you'll get refunded because you were "waiting so long"
Which it can work TBH, it just won't be a reliable method by any means
This is why there are spaces clearly marked for curbside pickup. If you're not in one of the designated spaces and try to pull this you will not get free food.
The apostrophe actually makes it a contraction, not possessive. So they're really saying "the underpaid teacher who bought it with it is own money". I know not everyone cares, but that's how our weird language works...