I cannot omit a Subtilty of one of those Quack-operators, with which he gull’d the poor People to croud about him, but did nothing for them without Money. He had it seems, added to his Bills, which he gave about the Streets, this Advertisement in Capital Letters, (viz.) He gives Advice to the Poor for nothing.
Abundance of poor People came to him accordingly, to whom he made a great many fine Speeches; examin’d them of the State of their Health, and of the Constitution of their Bodies, and told them many good things for them to do, which were of no great Moment: But the Issue and Conclusion of all was, that he had a preparation, which if they took such a Quantity of, every Morning, he would pawn his Life, they should never have the Plague, no, tho’ they lived in the House with People that were infected: This made the People all resolve to have it; But then the Price of that was so much, I think ’twas half-a-Crown; But, Sir, says one poor Woman, I am a poor Alms-Woman, and am kept by the Parish, and your Bills say, you give the Poor your help for nothing. Ay, good Woman, says the Doctor, so I do, as I publish’d there. Give my Advice to the Poor for nothing; but not my Physick. Alas, Sir! says she, that is a Snare laid for the Poor then; for you give them your Advice for nothing, that is to say, you advise them gratis, to buy your Physick for their Money; so does every Shop-keeper with his Wares. Here the Woman began to give him ill Words, and stood at his Door all that Day, telling her Tale to all the People that came, till the Doctor finding she turn’d away his Customers; was oblig’d to call her up Stairs again, and give her his Box of Physick for nothing, which perhaps too was good for nothing when she had it.
Daniel Defoe, A Journal of the Plague Year  (Penguin Classics, 2003), 32