Wiktionary
give away the store
alt. (context idiomatic English) To transact, trade, or negotiate badly, by paying, provide, or concede too much to the other party. vb. (context idiomatic English) To transact, trade, or negotiate badly, by paying, provide, or concede too much to the other party.
Usage examples of "give away the store".
When the ladies worked their way up to the duke, the tables were suddenly turned, and while we were trying to hold them back, they were trying to give away the store.
In the corporate world, it was always best to deal with lower-level twerps because twerps always wanted to make themselves seem important even if they had to give away the store to create the impression.