I know 下来 so far as complement for verbs of motion, e.g. 跳下来，走下来，攀下来，掉下来. In them, the first character of the complement conveys the meaning "downwards", the second the point of view of the speaker "towards him".
Obviously,下来 in 买下来 has a different meaning than obove, how is it used and how is 买下来 different from simply 买 ?
Do these sentence differ in meaning?: