hen customer cancels appointment or when deleting test appointments then you have to manually delete payments to those deleted appointments and also you have manually delete customer. There could be checkbox that those things are done also when deleting appointment. Of cource if customer have already had appointment then customer should not be deleted.
This would make it lot easier and faster to manage system and system would be automatically in very consistent state after appointment deletion on cancelation. After every update I do test booking just to make sure that everything is working and everytime I have to delete from 2 places at least (when not deleting customer for testing).