As another commenter noted, it would not be cost effective to lose a whole seat just to sell a few more drinks, overpriced though they be. But it seems like the

As another commenter noted, it would not be cost effective to lose a whole seat just to sell a few more drinks, overpriced though they be. But it seems like they could increase sales in sort of the same way by distributing free or discounted drink vouchers to a select few passengers, and effectively turn those real passengers into "purchasers".