When you don't plan ahead with markets your at the mercy of what is available. Sites need to be mapped out and new stalls need to be allocated. Previous stallholders should get in quick and confirm your sites so you don't lose them to a new person who may then keep it as they are now the current owner of that site and get first preference.
While we love to honour previous people we have sites to plan and need to lock in the financials so we can plan the advertising budgets to maintain the sustainability of the event. So make sure you tell us by the deadlines whether you want your site or not.