I had a short-lived Warwick endorsement... this was back when my old band were doing pretty well, we had a big festival appearance coming up, we had the album out, and were pretty active. At the time, a lot of Warwick's UK endorsers had slipped below the radar - Stuart Zender had left Jamiroquai, Glen Diani wasn't doing anything after One Minute Silence split up, and so on, so they were after new blood.
I got our manager at the time to send them our press pack, and they got back to me and offered me an endorsement... this wasn't a full-on "free basses" deal though, more like a 60% off list price deal. So I got a Streamer Jazzman... and really didn't like it (horrible, horrible, baseball-bat neck).
In the end, I told Warwick I wasn't interested in pursuing the endorsement anymore, and sold the Jazzman for more or less list price. Thank you Warwick!
Basically, you have to be actively gigging in reasonably high-profile situations, with some visibility at gigs and in the press. You need a good press pack, and a tenacious manager to chase it up.