I'm of the philosophy:
Be polite.
Be professional.
But have a plan to kill everyone you meet.
I don't assume someone who is openly walking down my driveway is out to get me - but I'm prepared for it. Albeit, not as much as if I were holding a position in a combat zone, but prepared nonetheless. I'd be helpful and friendly to the extent of my ability, without unreasonably jeopardizing my safety or opsec.
In this scenario, I would already be armed with a pistol. If there's someone home with me I would alert them if reasonable (I wouldn't, for example, immediately scream out to the barn from the house that I've got a contact). I would first observe the surroundings to determine if there was any other threat or unusual objects/behavior in an effort to ascertain if they were truly alone. I would also confirm they don't have a long gun.
I would come just outside the house (a gesture of goodwill) and let the stranger approach to a comfortable communication range, no less than 30 yards. I'd feel pretty safe at that range, because I'd be right near the door to a lot more firepower than they would have, and it's damn hard to hit an erratically moving target with a pistol at that range for the majority of folks. All the while I would already be talking with them, and if anything had raised any concern I would have instructed them to "wait right there." Non-compliance after a repeat of the instruction would result in escalation of force. However, I expect most folks to be generally kind and reasonable, so after determining that what they need is something I am willing to offer - including casual chit chat - I'd happily oblige. The stranger would not be allowed inside.
Now,
I pose a different scenario:
What if it were at night, cold and raining? The guy says he locked his keys in his car while changing a flat a half-mile down the road. No obvious weapons, he doesn't seem shifty, just cold, tired, mildly upset, and wet. What would you do? I have a hard time answering this myself, and I hate to say (from a tactical perspective), but I expect I'd size him up, ask him some direct questions (name, where he's from, if he has any weapons on him - looking for honesty here - and a photo ID). I would explain that I'd be happy to help him, but that my safety is my priority, to which I would expect he appreciate and understand. If I felt comfortable and in control of the situation, I would likely invite him in, get something to dry him off, warm him up, and figure out how to get him fixed up. Possibly some brandy as well, because being cold, wet, and in a pickle sucks, and we've all been there.
The end of me may be my kindness, despite a reasonable level of safety. However, I'd rather live in a world where people are generally warm and accepting than cold and suspicious, and to make that world I have to be it.