For me, the best thing would be to stay courteous but not intrusive. I would say "hello". If they did not respond then I would ask "do you mind if I try to catch some of your fish?". Most of the time there isnt an issue. If they seem less than friendly then I just move on. I understand that I have the right to fish the dock but why would I start problems when I could just as easy avoid them. They have the right to be fussy and I have the right not to deal with it.
On the otehr hand, in a tournament situation, if I felt like I needed to fish the dock then i would exercise my rights as non obtrusively as possible.
Remember we represent all of us when out on the water.