A fair swap

Sarah was reading a newspaper, while her husband was engrossed in a magazine. Suddenly, she burst out laughing.
"Listen to this," she said. "There's a classified ad here where a guy is offering to swap his wife for a season ticket to the Liverpool games."
"Hmmm," her husband said, not looking up from his magazine.
Teasing him, Sarah said, "Would you swap me for a season ticket?"
"Absolutely not," he said.
"How sweet," Sarah said. "Tell me why not."
"The football season's more than half over," he said.