I had only 1 excursion with a gate agent that wasn't following the rules. It was on a commute from my home airport, and it was on one of my company a/c. I knew there was 1 seat open in the back, we have priority over others, even mainline, on our airplanes. She would not give up the seat, saying the flight was full. When they started boarding I counted 49 people get on the plane, so I politely asked her again for a ticket, which she said nope sorry. About this same time around the corner comes a mainline flight attendant, she didn't even have to stop and she was handed a ticket and down she went. Again I politely said to the agent that I had priority over her, as it was my company operating the flight.....followed by a nasty look and a "NO YOU DO NOT!" So a quick call to dispatch, followed by an ACARS to the crew, followed by the CA coming up and explaining to the agent and I was on. This gate agent is no longer a gate agent, and talking with the other agents (which I have come to know pretty well) they had said she was "asked to resign" due to her letting her friends on out of priority, as well as "sneaking" non-rev's on before paying pax.