We will never, ever be friends.
In fallout 1, the trick is you raise your barter to the point where your stuff is worth more than theirs. Get a bunch of SMGs or something, and trade them half of them. Proceed to take anything you actually want from shop keepers.
In fallout 2, killing bands of raiders is extremely lucrative. Also there are shopkeepers in San Fran that have all the high end stuff on tables that you can steal from. I stash neat items in the car, and only carry what I actually use because of how easy it is to get a hold of anything you need.