I used to send reminders, but n ot an ymore. Most of my items are BIN and 95% pay straight away via paypal. If someone doesn't pay or complete checkout, I send invoic e after a couple of days as a reminder and in case they are actually waiting for an invoice,

keep in mind if someone pays via paypal, even if it is for a combined purchase, the clock starts ticking on late shipment defects, so don't hold back to combine