Laudator Temporis Acti

Essays by the Late Mark Pattison, Vol. I (Oxford: Clarendon Press, 1889), p. 85 (on Robert Estienne):

The life of the printer, a life practical, industrious, real, if ever life was, has however collected its legend in passing down the current of biography. Nay, as in the case of other saints, the legend is more widely known than the facts. Such is the fiction, that he hung out his proofs at his street-door, offering a reward to any passer-by who could detect an error of the press. This apocryphal anecdote has even found its way into history. It may be found in other Histories of France besides that of Michelet¹, who is but too careless as to his authorities.

¹ VII.208.

Donald E. Knuth, The Art of Computer Programming, Vol. 2: Seminumerical Algorithms, 3rd ed. (Reading: Addison-Wesley, 1998), p. vii:

I have corrected every error that alert readers detected in the second edition (as well as some mistakes that, alas, nobody noticed); and I have tried to avoid introducing new errors in the new material. However, I suppose some defects still remain, and I want to fix them as soon as possible. Therefore I will cheerfully pay $2.56 to the first finder of each technical, typographical, or historical error.

Knuth makes the same offer in other books, e.g. in Ronald L. Graham, Donald E. Knuth, and Oren Patashnik, Concrete Mathematics, 2nd ed. (Boston: Addison-Wesley, 1994), p. ix:

We have tried to produce a perfect book, but we are imperfect authors. Therefore we solicit help in correcting any mistakes that we've made. A reward of $2.56 will gratefully be paid to the first finder of any error, whether it is mathematical, historical, or typographical.

In the event that there aren't new editions, Knuth posts corrections on his web site. I doubt that Knuth's bank account suffers much by payment of these rewards. First, he is so careful and painstaking that he makes few mistakes. Second, I suspect that most of those lucky enough to receive a $2.56 check from Knuth don't cash it, but rather save it as a prized possession.