Fallout 4 players now have to abuse the economy the old-fashioned way.
This wasn’t a matter of cleverly leveraging the game’s economy, but capitalising on a weird bug which prevented you running out of ammo when selling it to a vendor. You could clear out all their caps, and their entire inventory, and repeat the process at other vendors until you were sitting on a huge pile of loot and money.
Well, that’s all over; although Bethesda didn’t mention it in the notes, the first major Fallout 4 patch fixes that little exploit.
Back to working out what loot is most valuable by weight and investing in perks that decrease prices and increase vendor cap limits. Although you could always take your console offline and not install the patch, I guess.