Technically, I think it's just a preauthorization of what your estimate is; and they call if it costs more than that.
I think I slapped down $10 on a totally worn-out 84mm Craftsman, and less on a Pioneer (broken awl), and a mess of a SwissTool.
I got billed just that, and the Craftsman was fully rebuilt, and the Pioneer and SwissTool totally replaced (and I got the old ones back--put the Pioneer to use as a work knife, and the SwissTool honestly I wish they'd kept).