I'm an ASE certified mechanic as well as ASE certified in parts sales. Having worked for O"Reilly (and Buick and Honda and Checker and more stores than I can recall over the decades) and currently, happily working for CarQuest Auto Parts, I have to agree with the "don't trust anyone under 30" concept. There are great counterpersons and pathetic counterpersons at any store. The way a corporation treats their employees has a direct relationship on said employee's efforts. (Did you hear that, O'Reilly's?) I really like my job particularly because I know I'm helping people who actually need my expertise. Asking me for Cummins spark plugs, Halogen fluid and '71 Beetle radiators really ticks me off. I hope that post was a joke. Essentially it comes down to MODEL, MAKE AND YEAR which many people (even shop managers!) surprisingly don't even know and expect me to be psychic.