First: This advice is NOT for the people who let their families do the matchmaking. In that case, everyone is damn well sure they know each other, that's the whole POINT!
Now many readers write to me, asking me my thoughts on this matter. And I say, I would never get in between someone and their mother. That's rule one. So if your mother wants to pick your dearly beloved for you, I"m not going to tell her no. If you don't like it, YOU'VE got to tell her yourself with no help from yours truly.
If you are in that boat, the one that the families involved all have an oar, when the happy couple starts to row, it should be in the same direction. I'm not saying it makes things easier on the couple. It does make things easier on the families. Not the same thing at all.