I have been rejected three times, and I actually think the reason is that the panel of hosts covers pretty much what I could offer, so I stopped applying. (Even though my specialization in TV tunes is still without match ;) )
So unless you are very innovative or play a style that isn't covered enough (I guess they are looking for classical or flamenco guitarists) your chances are quite slim. But keep posting, and tell people when they have a question in the forum, that's what I do... If you wanna see my tricks, just type 'herve' in the search box...