Would you believe the Would You Believe gag cards have nothing to do with Get Smart?

Was the “Would you believe?” line from Get Smart once so popular it justified knock-off “gag cards” that were careful to make no mention of that program? I confess that show was a bit before my time, and though I’m familiar with its classic trope — one popular enough to survive all these years — I’m skeptical that it was ever sufficiently red-hot to make the items advertised above viable. Authentic shoe phones I could see, but this?

And the quality of the “humor” therein isn’t helping said viability either. A buck for a hundred sounds like an overcharge.