Seriously lol. He'd probably reduce more weight by taking his shoes off before he gets in the car.
At first I was thinking it's a good trade. Both cars are nice, but the Subaru being newer and less miles was a plus. Although now I'm having second thoughts after reading further and seeing this "weight reduction" bullshit, and manual boost controller? It just seems kinda sketchy.
Whatever you do, make sure you investigate the car THOROUGHLY and ask the owner a lot of questions before you trade.