I started at record stores... made frequent trips down to Chicago (a 3 hour+ round trip) just to buy the stuff you couldn't get here (anyone from the area knows about Gramophone Records!). Then in the late 90's to the early 2000s I was in 2 record pools, plus got music from the radio station I did commercials and 5 o'clock mixes for and some of the studios that weren't part of either pool I was in. Like AHD said, they come and make sure you are who you say you are. Obviously I did radio stuff, but some of the label reps wouldn't work with me until they had someone physically come down to the club I was spinning at.
My record pools were great, but you had to weed though a TON of crap that they were trying to push just to get to the good stuff. For every Cash Money record (they were SUPER big back then) you had 10 records of people like "The Ghetto Blast Mob" who had just HORRIBLE records. Makes you wonder how many acts these labels actually sign and never go anywhere.