What Order Management software are you using?
I think the way Marko described would work in absence of full-fledged order management software but I think it'd be a lot of work without a full time accountant (in QB I think a lot of people sales in daily batches so you'd have to narrow it down to the per-order level to really get it to work well).
Our order management software has an option to create returns/exchange and specify the reason. You can then run a report on this. It's a small enough problem for us though that I've never really used this feature but like you, I'm starting to think it's a good idea to start implementing some sort of tracking.