@a45heaven 

So why did they give permission for the cancel order and relist workaround then?

By the new terms and conditions alone, they could have refused that.

& as they seem to be taking refunds from seller available funds and potentially straight from their bank accounts (following that logic train through) and not from the pending funds specific to the order in question, surely it would have made more sense based on your reasoning for them to simply allow full payment and partial refunds afterwards as the only form of combining sales.