But in practice it was interpreted imaginatively

From the excellent Perilous Fight by Stephen Budiansky, an account of the naval aspects of the War of 1812. Page 52.

“But even that threat could not keep more than six thousand men from deserting each year, willing to risk the chance of draconian punishment rather than the certainty of the continued brutality of life aboard a man-of-war. Between the deserters, and the new ships to be manned, and the fifteen hundred men a year invalided out of the service from injury or sickness, the Royal Navy needed to find close to twenty thousand new men a year. A semibenevolent patriotic organization called the Marine Society offered to outfit destitute boys and men with a new suit of clothes and a few days of good food and tutoring if they would volunteer; that provided a thousand a year driven mostly by desperation. A few dreamy, naive young men from working families were drawn by visions of adventure—“I had read Robinson Crusoe many times over and longed for the sea,” said the son of an Edinburgh cooper who enlisted. But most of the “volunteers” were the so-called quota men that the magistrates of each county had to produce in two large drafts in 1795, supplemented in the following years by a steady stream of various small-time thieves, beggars, pickpockets, and other local nuisances from the local jails, including the occasional dissipated scion of a gentlemanly family who had fallen into drink, debt, or other dissolution that made getting out of the country as quickly as possible an attractive option.

Volunteers, willing and otherwise, could satisfy only a small fraction of what the navy needed during its rapid buildups. By 1800 the Impress Service was a permanent institution, commanding the full-time services of one admiral, forty-seven captains, and eighty lieutenants whose job it was to make up the difference. “Gentlemen,” officers of merchant ships at sea, and sometimes fishermen were exempt from the press, but otherwise the law permitted the navy to forcibly take any “persons using the sea.” That generally meant merchant seamen, but in practice it was interpreted imaginatively. Impress officers routinely declared that a man who had just been dragged in off the streets of a seaport town “looked like” a sailor, and that was good enough.40 Merchant ships at sea were in many ways the favorite target of the press, however, since they were sure to contain experienced sailors. A Royal Navy captain almost never passed up the chance to press a few “prime seamen” from a passing ship.