buy something
Fig. to believe something someone says; to accept something to be a fact. It may be true, but I don't buy it. I just don't buy the idea that you can swim that far.
buy something (from someone) (for something)
to purchase something from someone at a particular price, or for a particular type of payment, such as for cash, for practically nothing, etc. I bought the car from Mark for a reasonable price. I bought it for a reasonable price from Mark.