These marks are from the sights being installed...and not in very profesional way. However there is no way that corrossion will set in, as Tennifer is a steel treatment, not the finish. You can wear out the finish, but the metal still will be protected. Glock is super easy to work on, so just check all the critical components (firing pin, trigger, magazine release button) and you good to go. If you are not sure about the condition of the pistol on EE, detailed pictures may help a lot. Indeed "excellent" or "like new" description is very different for different people. In fact I've got a few flukes myself, even from "reputable" dealers. When it comes to the used guns it's like lottery. May go great...or you may lose your money. Good luck!