When and how did the Beatles turn professional?

Answer 1

They failed a Larry Parnes audition to back Billy Fury on a tour of the UK in the spring of 1960 (stories differ; most accounts say it was because of Stuart Sutcliffe's lack of ability on bass guitar, Parnes recalled later that their then-drummer, Tommy Moore, was a mismatch for the group), but were invited later to back Johnny Gentle, another Parnes act, for a two-week tour of Scotland. Until then, they had called themselves "Johnny and the Moondogs", but became the Silver Beatles for the tour.

Lennon and Sutcliffe were in Art school and simply cut classes for two weeks (heisting an amplifier that belonged to the school, to add to their equipment); Paul McCartney persuaded his father to let him take the time off high-school, to "give his brain a rest" before final exams. George Harrison was an apprentice electrician at Blackler's Department Store in Liverpool, and had to take his summer vacation early, Tommy Moore, employed by day at Garston Bottle Works, also took time off his job. (He quit the band, once they returned from Scotland.)

In August of that year, Jacaranda owner Allan Williams arranged a full-time booking for the band in Hamburg; drummer Pete Best was available, and joined on short notice, and the band formally adopted The Beatles name. (A three-week engagement turned into five months, playing in three different Hamburg nightclubs along the Reeperbahn.)