1. Rolex DOES NOT ISSUE CERTIFICATE, they will only issue you a receipt and tell you verbally that its a real or fake one after they authenticate the watch. The 75 you paid for will include a cleaning cloth and small Rolex pouch. Seems that the myth that you will get a certificate has been around a lot as when my wife went there, they told her that this myth has been going on since ages. They told her that Rolex cannot give you a cert as there is no telling what the person can do if a certificate is issued, he/she can just remove the internals and swap in a non-Rolex movement, ie. ETA/Valjoux movement and then sell it off.
2. There is a small area which is viewable by the public that allows you to see the authentication process taking place and you can see basically how they handle the watch. Enter the main building and turn to your right to the reception. (You will get a cold one though regardless whether your watch is real/fake, new or old)
Checks will be done on the dial, bezel, etc. They will also check on the serial number between the lugs and open up the case with a rolex tool to look at the movement/inside case back, etc. When in doubt, they will remove alot of the stuff inside to check. This may take anything from 15 minutes to half an hour so you can seat and wait in the comfy chairs that they have there in the viewing area.
3. All you will get is the receipt stating the serial number of the watch, so if its a fake one, you will see that the serial number isn't the rolex series or they won't put it there at all (in cases of cheap fakes as they don't have it there)
4. Feedback on them from some friends, they will not retain your watch even if its found to be fake but you will get weird looks from them. Service from them are not really good even if you are a genuine Rolex customer.
5. AD = Authorised Distributor, basically retail shops which are the authorised folks to sell new Rolex watches in Singapore.
6. The Rolex building at Tung Building itself does not sell watches, beside the buiding are Paragon, etc and nearby is the Lucky Plaza shops where some of the ADs are.
All they do at Tung Building is for you to service/repair your watch and to authenticate the watch.