CSO return shipping charge

I check inventory for parts sitting on the shelf more than 11 months but less than 12. Then I go to the shelf and check the tag if they are RIM, CSO, DRO, or QPO. If they are CSO I check why they were not installed. I let service, bodyshop, or sales know I am charging them 35% restocking fee. So I apply for the CSO return. (usually 3-8 pieces)[is that normal or more than average?]
One of the pieces is a $2.07 part. By itself not really worth sending back but in the group I'll add it. In comes the paperwork and all is fine. They usually break it down as to scrap, local warehouse or back to CCRC 624. The $2.07 piece is slated for CCRC 624. Subtract the 35% fee -$0.72 and were down to getting back $1.35. Nowhere did it list a shipping charge. Today I check the invoices and BAM I see they charged me a shipping fee of $4.00
I did not see any shipping charges listed so I figured I was good. Going forward what is the best way to see if I am actually going to be charged shipping?
Thanks Dave
One of the pieces is a $2.07 part. By itself not really worth sending back but in the group I'll add it. In comes the paperwork and all is fine. They usually break it down as to scrap, local warehouse or back to CCRC 624. The $2.07 piece is slated for CCRC 624. Subtract the 35% fee -$0.72 and were down to getting back $1.35. Nowhere did it list a shipping charge. Today I check the invoices and BAM I see they charged me a shipping fee of $4.00
I did not see any shipping charges listed so I figured I was good. Going forward what is the best way to see if I am actually going to be charged shipping?
Thanks Dave