If store or admin want to charge different fee or we can say a pickup fee it should be provided with an option. This will be good if there are special packaging or staff is appointed for handling self-pickup orders.
Order scheduling will be important aspect for self pickup so store owner will know about the pickup date & time of the day. Also the self pickup order collection by customer needs to be confirmed via pin for marking order as picked up or complete.
The self pickup system also needs improvement in the payment flow as the order payments will be directly collected by stores but admin can only earn with self pickup when an invoice is raised by admin to stores for commission on self pickup orders.
The amount commission should be displayed for self pickup orders & charged automatically by system weekly or monthly using payment gateway without too much manual involvement. Non payment of commission within specified time then stores should be disabled by system.