sell bargains

I have a bridge to sell you

An indirect way of expressing that the addressee is gullible.

one of His Majesty's bad bargains

An incapable (sick, etc) or incompetent soldier.

sell dearly

To make one's opponent pay a very high price to defeat or obtain (a person, unit, vehicle, or territory).

sell down

To betray a person; to conspire against someone for personal gain.

sell down the river

To betray, especially in a manner which causes serious difficulty for the one betrayed.

sell ice to Eskimos

To persuade people to go against their best interests or to accept something unnecessary or preposterous.

sell like hot cakes

To be sold in large numbers quickly.

sell one's birthright for a mess of pottage

To make an unfavorable exchange, especially of something of great, but deferred value, for something of very low, but immediate value.