How Does One Authenticate A Rolex

[Rolex Freak]

Hello All, I'm just wondering how you can authenticate a Rolex watch without paying Rolex. Can't you take the serial number to the dealer and have them determine whether the watch is real? I was told today that it would cost $150.00 to authenticate the watch and it would take 4 days. If i'm interested in buying a watch, i don't want to have to dish out the money and then it's not real. When i called to provide them with the "M" serial number, they Rolex Canada wouldn't help me over the phone. Please help. Thanks.