William Carey married Mary Booker at Sevenoaks, Kent on 7 December 1767.
Their daughter Sarah Carey was baptised at Buxted 26 December 1769.
Mary Booker came from Buxted, baptised 29 May 1743, daughter of William and Sarah.
William Carey baptised at Hooe, Sussex 17 February 1740, son of Thomas Carey and Elizabeth (Wenham).
Lots of people on Ancestry have a marriage between a William Carey and a Mary at St Leonards parish, Shoreditch, London. Probably they are confusing St Leonards parish with the place St Leonards-on-Sea in Sussex.
I really can't understand why people just copy trees on Ancestry without checking. They end up with a tree full of people to whom they are not related!
Best wishes
Caroline