If it had been sold, he couldn't have bought it.
No bought tickets had been previously sold.
What's your point?
The took advantage of an oppurtunity to sell a unsold ticket by use of force to someone who already had a ticket, for circumstances that did not require him to purchase an additonal ticket.
In other words, they saw a fat guy, and decided to force him to buy another ticket, when they knew dang well, that they would have extra seats.