Hogwash! Usually, you can work with sealed bearings just fine. Sometimes you do need a bearing press to seat them, but most of the time they just pop in and out. On cartridge bearing hubs, it is possible that the axle nut is a little loose. You adjust it much like a cup/cone: there should be an adjuster nut (in place of the cone), and a lock nut. If that doesn't work for you, then you can replace the cartridges... they're cheap. You can use the axle to tap each one out of its socket, and you just press fit the new ones in.