staff salaries rise every week. the rise % depends on the level of the staff. lvl7 have their salaries raised much more steeply than lvl4s and so on. but every lvl4 get the same % rise every week. when you buy a new staff you bid knowing how much their salaries will be. usually a lvl 4 with a 10k salary will receive lots of bids while a lvl 4 with 60k salary won't be sold or will be sold by 1k. and so on.