Unofficial Expo Guides or Fair Guides have been around for decades, but still find new victims year after year.
According to the FTC, a recent complaint included an operation that would send mailings to businesses who attend trade shows.
"The mailings mention a specific trade show or exhibition and are designed to appear as though they are merely asking the recipient to update and check the accuracy of information for the “exhibitors directory” for the named trade show or exhibition.
...the mailings include a form stating that the recipient’s basic information has been listed in the directory for free, and instructing them to confirm its accuracy or make corrections on the form...Many recipients do not notice a statement, buried in fine print at the bottom of the form, that by signing and returning the form they agree to pay the defendants $1,717 per year for three years.
...long after the form is signed and returned and the defendants’ 10-day cancellation period has expired, the defendants send an invoice demanding payment of $1,717...late payment notices follow, with late fees added, and some organizations pay just to end the harassment."
Because processes and procedures can very widely in other countries, even seasoned international exhibitors can fall victim to scams like these.
The best way to protect yourself is to contact the show organizer and let them know what you've received before filling out anything. The organizers can let you know if what you've received is legitimate.