I have. Guy was a park employee. Pretty sure it was disney at the time. Several years back. He had my tickets arranged for pick up at the kiosk. The lady just handed me my 6 tickets and said have a nice day. No payment. I met him inside the park almost an hour after we went in. In hindsight, I could have fleeced the guy. For a family of 6, on 3 day park hoppers, pretty sure I saved myself a decent amount on regular price. I paid him $600 cash for the tickets as I recall. Downside is carrying cash, the risk of not knowing who it is you are meeting, and really screwing up your vacation. My plan B was simply to buy park tickets at regular price. Would I do it again? If I knew the guy was meeting me in the park, then yeah, probably. I am a risk taker, I guess.
Since then, I have shopped around for the best deals I could find at either Uiversal or Busch Gardens thru more traditional means.