Price Breaks and Partial Shipments?

Well ,Lets us see how we can connect these in a business scenario

I was discussing with business and we wanted to setup some price break for items .Lets say if the customer orders 1-100 the price is 150 and 100-230 is 100 dollars and

Lets say the customer bought 150 unites @ 100 dollars and suppose he wants to return 50 units
The system would suggest to give credit for 50 @ 150 which is 7500 which is 2500 more than the sold price

Well ,we might argue to use refrenced RMA's ....But these pratcial problem can still exists ....