When Mercenary's move slow in the field and react slowly. Also if you put in some appearance in the campaign you will disobey no orders and get paid.
Surrender
A merc unit can surrender in battle in order to survive to see another day. this can happen if the unit is left out to fry by the employer leaving them stranded. If a unit does this too much their reputation will suffer.
Changing Sides
In any campaign a mercenary unit that is greedy can changes sides at a vital moment in battle. They might succeed over their former employer but they will be almost untrustworthy to victor. they way Mercenary units do this is by asking for the cash before they change side so that the mercenary unit will do it or play both sides and remain loyal.
Bribes
A bribe occurs when the enemy pays a mercenary unit for information, lapse in military security, or even helping the enemy out in battle. This venture is risky but you will make allot of cash.
Plundering Locals
Mercenaries in Garrison, security, and cadre duty can add to their income by plundering off of the locals. By using low-key protection rackets to outright plundering. Since employer do not like their mercenary units doing this to their people, mercenary units should only do this on backwater worlds or recently conquests of planets. Another way is to incite a open rebellion on the planet and then crush it and destroy all of the evidence.