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All of the different gens have different contracts, and within them the individual talents have different contracts as well. There's a base that they start from in negotiations and certain subjects that are soft or hard. After the contract period, which is apparently a year, they renegotiate a new contract and it changes more.
Gen 1 collectively negotiated away from having a base salary for a higher cut of donos and other stuff. Invaders work under a different system as well.