Warn when receiving more quantity than ordered
When receiving goods the user has to edit the quantity but sometimes he may make mistakes like putting or forgetting the decimal. This can lead to receive much more quantity than actually. Such mistakes are quite complex to solve because the workflow step can not be undone. So the user has to make a return. But this can have an impact on the average cost price if there are some landing cost because the landing cost is diluted.
So the idea is to warn the user when he is receiving more quantity than purchased. I do not think we need to deal with a tolerance rate because it is just a warning against mistakes not a feature to tolerate mistakes from supplier. I do not think either that we should warn for returned products because there is the assignation process which ensure that the quantity picked exist in the warehouse (so it can not be wrong by multiple order of magnitude).
The same applies to receiving returned sold products.