what criteria does the Squire have for putting a crew together?Why does he trust Long John Silver?

“‘It was the crew that troubled me. I wished a round score of men—in case of natives, buccaneers, or the odious French—and I had the worry of the deuce itself to find so much as half a dozen, till the most remarkable stroke of fortune brought me the very man that I required. I was standing on the dock, when, by the merest accident, I fell in talk with him. I found he was an old sailor, kept a public-house, knew all the seafaring men in Bristol, had lost his health ashore, and wanted a good berth as cook to get to sea again.’”

He trusted him because he'd told him that he lost his leg in his country's service.

"Long John Silver, he is called, and has lost a leg; but that I regarded as a recommendation, since he lost it in his country’s service, under the immortal Hawke. He has no pension, Livesey. Imagine the abominable age we live in! Well, sir, I thought I had only found a cook, but it was a crew I had discovered."