They show you the exit . You can’t go in making demands. Find a place with very flexible schedules and a good ability to drop / swap trips . Get in, learn the system and make it work to your advantage. Will you get everything you want 100% of the time ? Hell no , but more often than not you can get something you can live with.
You go in making demands, no matter how much they need you , they will pass you by and go to the next guy . You’ll be the butt of many jokes during the Human Resources lunch break .