New Score

I have a B-body 8.75 rear end with 355 SG 489 case
I just went and bought a A-Body 8.75 276 gear 489 case.
Complete Drum-Drum.
Asked the guy what you want for it. He said its not worth anything cause of gear and
open gear. He said make me a offer and I told him 75.00. He said sold
so I jerked his arm off and loaded it up. I kept my mouth shut and poker face on.

Whats your thoughts. Should have I been honest with him.
Or take advantage of stupidity