Chet claims to have been to the New Vegas Strip twice in his life. Both times he apparently drank a lot of liquor and lost most of his caps while gambling, in that order. He speaks fondly of the city however, but he also warns you not to stir up any trouble on account of the NCR and Mr. House's securitrons.
The player randomly can find all the weapon mods for the varmint rifle, the 9mm pistol, and the .357 Magnum revolver in his shop inventory. If no mods are available, wait for the store to restock (4 game days). You might have to buy a previous mod for a new one to be stocked.
Killing him after Run Goodsprings Run grants no Karma gain or loss.
He is generally a good merchant early on in the game, as he carries a wide selection of low to mid level equipment and general use items. However he will become less useful the farther you go into the game, but he does provide a decent assortment of early essentials.
If you have a mixed reputation (at least "Mixed") he will give you a 75% discount because you remind him of himself when he came to town.
ps3xbox360 Chet will not restock, even after 200+ in-game days. The only item refreshing is special ammunition. You can get his stock to refresh by saving in the store, quitting the game and loading with "continue", simply loading a quicksave will not work. [verified]