That used to happen to my husband. He took charge of organizing inventory in his store, and knew it so well, that when someone called to ask for something, he could tell them, with about 99+% accuracy and without referencing the computer, if it was in stock.
People used to get pissy and ask for the manager (he was ASM) if he answered without pausing to look. And invariably the manager would say, "If he says we don't have it/do have it, then we don't/do. He would know."
(Only time he's ever been wrong was when the game came in just before shift, and he got the call before he got to check the new games and put them away.