Before two passengers flew from the United States to Toronto last month, they submitted required copies of their vaccination cards and negative coronavirus test results to a portal reviewed by Canadian authorities.

One listing offered eBay customers an "Authentic CDC Vaccination Record Card" for $10.99. Another promised the same but for $9.49. A third was more oblique, offering a "Clear Pouch For CDC Vaccination Record Card" for $8.99, but customers instead received a blank vaccination card (and no pouch).