How to know if a guy is nice? Just met him..?

So, my best friend liked a guy for 2 years in high school, and then after school, they started dating(3 weeks, met 3 times). There is a vast cultural difference between the two, and I wanted to know if I could see if he is a nice guy or just play-acting, because he always seems nice around us, sometimes just too nice. But their cultural differences show when they are around, with a very vast difference in their points of view. True, if he really is a nice guy, they could go on, but how do I find that out? I know the trick about seeing how he treats his inferiors, but he just treats them neutrally, neither good nor bad. Can I get any suggestions? Because my friend doesn't want to continue if for all her effort, the guy later turns out to be bad..

Thank You,

Khushman