Sales invoice Price difference

Hi gurus,

Please help me to solve this scenario.

I sale 10 units material for 100 each price to my customer.

But due to some problem if he returns my material.When we Replace the material there is a Price Difference.

we are using Moving Average Price.

Now I want to sale that material again for 90 each price that will be less than price 100.

The main issue is: “ I can not change the (financial postings)invoice price when I replace the goods, this is legal requirement here”.

How would I handle this price difference.

Please help.

Regards,

George