Six ways to learn everything you ever need to know about a man before you decide to marry him:
Watch him drive in heavy traffic.
Play tennis with him.
Listen to him talk to his mother when he doesn't know you're listening.
See how he treats those who serve him (waiters, maids).
Notice what he's willing to spend his money to buy.
Look at his friends.
And if you still can't make up your mind, then...