I agree with your skeptic.  I don’t think the third party will be able to claim a charitable contribution deduction because it is a “quid pro quo” for the lower purchase price and not voluntarily given without the expectation of personal benefit.  But it is worse for your board member.  He will be deemed to have sold the property for the dollar plus the “contribution.”  If that totals more than his tax basis in the property, he will have a gain subject to income tax, without the cash from the transaction to pay it.  It will have to come out of his pocket.  It is not entirely clear that your director will be able to take a deduction for the amount transferred by the third party to your organization.

The most tax-efficient way to do this deal, assuming the board member has a built-in long-term capital gain, is to have him give you the property, take the full value deduction and let you sell it to get the cash.  If you don’t want to be in the chain of title, which may be a good idea if there is any possibility of environmental or other liability, let him sell it, retain the amount necessary to pay the taxes, and give you the balance.  You can do the deal he proposes, but neither the buyer nor the seller is likely to receive the tax treatment they expect.