blessed purchase

People prefer a deal to saving an amount of equal value.  This is true even in the limit case: people prefer an apparent deal of no value over saving an amount of some small value.

Of course, I'm concealing a telling idiom:  we usually wouldn't say "people prefer a deal"; we'd usually say "people prefer getting a deal".

And that's the clue to half the explanation: people register a deal as received, as an offer accepted.  The other half is that a deal accompanies a purchase - a wanted thing.