Wolfgang might act insane, but he only plays the madman for sales. His inventory is mostly random junk, making him useful for finding custom-weapon components or just cashing in gear for caps. Dialogue with Uncle Roe states that Wolfgang is aware that his choice of shop specialty is unusual and won't, in and of itself, draw a big crowd, so he adopted the persona of a rather eccentric traveling merchant to draw people in. He also considers his use of the terms "junk," "garbage" and other such terms to describe his wares to be a very successful marketing ploy, often using them to rather humorous effect.
Merchant Empire: Initially, Wolfgang has a Repair skill of 15, but investing via Uncle Roe into his caravan expands his inventory, and his repair skill jumps to 75. This allows him to repair to 85% condition. After the second investment, he rewards the Lone Wanderer with 5 to 7 Stealth Boys, depending on level.
Agatha includes a shout out to her "old friend" Crazy Wolfgang in her broadcast, saying, "No one can scour the Wasteland and find such oddities as you".
After fully investing in his caravan, he will then have the highest repair skill of all the caravan merchants. Equipping him with a repairman jumpsuit (reverse-pickpocket) will boost his repair to 80 (88% condition), giving him workman's coveralls will boost it to 85 (91% condition). However this leaves him vulnerable to injury or death, if you are not present when he dies you may lose the item you chose to equip him with when his corpse disappears from the game.
"Welcome, sir or madam, to Crazy Wolfgang's Traveling Junk Store! The Depot of Detritus, the Shop of Slop, and the Caravan of Crap! Now, what odds and ends can I, the Craziest of all possible Wolfgangs offer to you?"
"I hear you're the one who's so deeply invested in my junk. Not as deeply as me, of course, but who is, really? I picked up some Stealth Boys the other day, and they seemed like just the way to thank you for your investment. Kudos!"