wanted me to deduct every expense they had during their mission. I told them that I wouldn't deduct normal expenses like food, clothing, toilet paper, ect.. I could see the logic and find some validation in expensing additional rent and travel.

They deducted everything. The IRS audited them and threw out every single deductions except tithing/fast offerings. I don't know all the details but they had to pay back a couple hundred dollars. Like I said, it wasn't worth it for them. Some other case may be worth the risk.

They IRS is not going to be able to track the expenses to the charitable organization.