Agency is a terrible system. You will be dropped the moment they don't need you, that's the only guarantee you have. Each day you will be summoned as required and you had better obey or you will be added to the bottom of the pile of names used for calling people for work, unless they really need you, at which point they will be all nice and plead and beg you to help them. They will expect more of you than a overseer at a plantation. In fact, I'm pretty sure slaves worked less than what you're expected to work through agency. Sure you get paid these days so it's technically not slavery, but see how you feel after a 12 hour shift lifting up to 30kg boxes non stop and only a 30 minute break at minimum wage.