I believe this faction is crazy and not very good. But I like to find all the possibilities in Fallout. Now I wonder if there any other quests from Van Graffs after the massacre of Legion while selling weapons? What can Van Graffs give me except their weak armor and rifle?

Plasma Caster, Plasma Defender and Multi-Plas would be what you should be looking at.

Those are nice toys, and easily stolen right off the table with a little Stealthboy use

From what i got from it, after finishing the Legion, was the opportunity to come back now and then to check if they had items that needed to be transported.
Short terms: You're gonna be their UPS / DHL / delivery boy / girl.

Not worth it for me, so i'm gonna start over....by not killing the Legion

The only good option for me, as I understand it now, is to allow a man with a bomb come into their shop to demolish 'em. They say all the stuff on the shelves will be ruined, but still you can seach the bodies and on the second floor.

You can also just "Grab", by clicking the left thumbstick on the 360 to Grab then take them over to the toilet, stack up all the stuff you want and steal it all. No negative Karma and they can't see you as they don't enter the corridor with the toilets.

they can be grabbed without killing them?

I looted the entire store first time I went in there. Just right click the thumbstick, grab an item, and walk it through the door towards the bathroom so you're out of sight. You can then steal all of it without any negative consequences.

I used a stealth boy and stole every gun i the place the sold the crap back to them and if they put it back o the shelves i will do it again

You have to 'grab' the stuff, not 'take' it. Once you grab it, take it into the bathroom, drop it, then take it. No negative karma and you can ripp off the whole shop that way.

i let the crazy dude with c4 straqed to his body walk in sixy explosion i must say..