Like was said above we treat them all the same until they don't pay. Then a case is opened/closed.

We find that a large percentage (not all tho) of our non-payers have FB score of 5 or under, most often 0.

I think they forget that there is a 2nd stage to buying an item and that is to complete checkout.

Then they never come back and check messages. We always send a gentle reminder on day #3.

Then if no response on day #4 open the case. Rarely do they end up paying. So on day #8 we close it.