Question About The New Pre-order System

https://www.picturespro.com/sytist-manual/articles...

Hi Tim, I have just set up my first pre-order gallery and am very excited, it looks so neat on a mobile too.  In my case I am taking pre-orders as opposed to pre-rego.

My question is to what comes next.  I load up the passcoded galleries and sent myself a test and im asked to fulfil what I pre-ordered - makes sense .. then I go away.

But im predicting the inevitable "I want to change my order now".. and also wondering about upsales.  For eg: Jenny Smith pre-orders Basic Pack 1 for $20.. sees images and now wants the Huge Big Pack for $100.

I can issue coupons, encouraging a 2nd sale, but what if they don't want that order at all now anymore - what are my options?  Can I cancel it and issue a coupon?  What is best practice I wonder? 

Thankyou.