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:
pcps3xbox360 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]
pcps3xbox360 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 3–4 days then saving the game. Exit to the dashboard and then CONTINUE (not load) your game and he should have restocked.
pcps3xbox360 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]
pcxbox360 When selling things to Mick, he doesn't pay the full value of the object. [verified]
xbox360 He may not appear inside of Mick and Ralph's store. Reloading the auto save upon entering will correct this. [verified]
pcps3xbox360 He may not give you the Pimp-Boy 3 Billion, even after doing everything required for it. [verified]