A question about time travelers

If you met someone who claimed to be a time traveler, how could you possibly believe them? What could they do to make you truly accept that they could travel through time (forward and/or back)? For the sake of this question assume that you wouldn’t be able to travel with them to look at dinosaurs or into the future.

If they went back and change things I can’t see how you’d notice the difference and if they go forward and tell you something happens in the future you have no way to verify it.

I suppose they could go forward in time a brief period of time (say the end of a basketball game you start watching) and tell you the exact statistics but I think most of us would just chalk that up to incredible luck instead of the more incredible possibility that a person can travel through time.