Mick is a known source of a number of hard-to-find weapons in the Mojave Wasteland, particularly for explosives. However, most of these items are only accessible after passing the necessary Speech check to get access to his "special inventory". His standard merchant inventory consists of the following:
PCPlaystation 3Xbox 360 Mick's secret inventory is only added to his available items when initially unlocked. Once his inventory refreshes he will no longer carry the additional items. [verified]
PCPlaystation 3Xbox 360 His store inventory may never refresh, even after accessing his expanded inventory. [verified]
A possible fix is performed by entering his store, then without interacting with either person, save and quit the game. Then use continue to load. Mick/Ralph will have restocked. This applies to all other vendors as well. If this doesn't work try standing right in front of him, waiting for 3–4 days then saving the game. Exit to the dashboard and then CONTINUE (not load) your game and he should have restocked.
PCPlaystation 3Xbox 360 Sometimes, when you ask to buy from him, you will not be able to buy from him. He will simply say, "take a look" and then will go right back to dialogue. [verified]
PCXbox 360 When selling things to Mick, he doesn't pay the full value of the object. [verified]
PCXbox 360 He may not appear inside of Mick and Ralph's store. Reloading the autosave upon entering will correct this. [verified]
PCPlaystation 3Xbox 360 He may not give you the Pimp-Boy 3 Billion, even after doing everything required for it. [verified]