Smart move. If you had any input on the content of the card, that would give the customer an excuse to blame you if the mail campaign produced poor results.When customers came to me for a bulk mail piece - often a post card of sorts - they'd ask me what to put on it - how to word it.
I'm like; WTF! It's your business, not mine, how the F am I supposed to know?
I might have expressed that to them a bit differently.
But I would nearly always advise them to include some kind of giveaway, or coupon. It's astonishing the lengths people will go to if they think they're getting something for nothing.