I think the post from our new former FAM was very helpful in many ways, and I thought the tone was well-handled. However, I am just about sure that (s)he is wrong about the tax deduction. I do not believe that there is any industry in which you get to "write-off" revenue that you didn't get. That is, the following:

Hypothetical Statement for flight (sorry, I dont' know how to make it line up)

Income from passengers, mail, cargo $100,000
Costs (airplane lease, crew, gas, overhead) $ 92,500

Taxable profit (income less cost) $ 7,500
Less: 2 First class tickets we would have
liked to sell for $2,500 each, but a
flying FAM sat there instead $ 5,000

Taxable profit $ 2,500

That just doesn't sound right. You don't deduct "money you didn't get" as an expense. Nor is it likely that the airlines actually get a "tax credit" for that seat (if they did, they would be fighting to have 5 FAMs on every flight). Because taxes on $2,500 are, let's say, 25%, or $625. So if you got a "tax credit" of $2,500, that would be like selling the seat for $5,000.