My dad always used to give the card number but get one digit wrong intentionally.

If they are entering it in a computer, it won't work because the computer verifies that the card number can be valid (there's an algorithm by which credit card numbers are generated - it's not random).

In any case, I wouldn't think twice about it (especially if I intended to go). On the off chance that someone steals the number and buys a TV, you wouldn't be responsible.