Dollar value declared on glider bill-of-sale

I'm buying a glider and the seller wants to declare the price paid as "$1000 and other good and valuable consideration". The actual sale price is $28,000. The seller wants to do this because when he bought the glider years ago he used the "$1000 and other good and valuable consideration" phrase on the previous bill of sale filed with the FAA. He doesn't want to declare the actual sales price on the FAA form and then have the IRS come after him for a capital gains tax. The seller can only see things his way because "this is the way that he has always done it."

My question is: if I go along with the seller's white lie, will I pay the price down the road when I sell the glider for say $25,000? Will the IRS come after me for a $24K capital gain?

Does the FAA automatically share the bill of sale value with the IRS? I live in a state with no aircraft registration fee/tax so there is no declaration of the value of the glider to my state.

The FAA bill of sale form does not require my signature, so it is only the seller that is going on record and misrepresenting the price.

I have some other documentation that establishes the price of purchase at $28,000 so should I show that to the FAA at this time? Or should I wait until a potential problem comes up years down the road.