writing off reimbusements

So I have done some research in the IRS's website, mainly in publications 334, 535, & 463, what I came up with is there are certain circumstances that reimbursements can be written off, but cannot for the life of me find out what these certain circumstances are. It has to be in there somewhere, but I haven't been able to find it within the tens of thousands of pages.

 

If the reimbursement shows up on you 1099
as income (unlikely)
than it would be deductible.

 

I have always insisted that Lumpers and other reimbursements are NOT included in my income, because it is NOT income

So if i make $1,000/wk, i pay taxes on $1,000/wk

if a include a lumper fee of $200. then i made $1,200, but i cannot claim the lumper fee of $200, so basically i have to pay taxes on $1200 though i never made that money

so the shipper (or whoever) gets to claim that $200 lumper fee and i am stuck holding the bag on a $1200 income i never received nor can i claim the deduction