Well, he has a point... If the battery has good voltage, then it is likely not the battery or alternator.
Could be a bad starter, ignition switch or wiring... Gain access to the starter and see if the big cable going to it has +12 volts, make sure the engine is grounded, and, while having someone turn the key, see if the small wire to the starter has +12 volts also. If those three conditions are met, its the starter... If no +12v on the big wire, starter wire is bad, if no engine ground, ground strap is bad, no +12v on the small trigger wire, then it could be fuse, ignition switch, something in the neutral safety switch, etc...