Technically a wall Fish is not part of the installation, reguardless if the plate is already there and if all the technician has to do is re-pull the wire. A Wall Fish is considered a wall Fish, reguardless if its already half way done before hand.
Its just like as if you went to a car wash and paid for a full wash with the interior and exterior and you had already vacummed out the front of the car. The car wash place is still going to charge you full price, eventhough the interior was only half done.
Yes this is something the installer can technically charge for.
But I do agree with your point. What really pisses me off about alot of these installers is that everything is one sided in their favor.
A perfect example is the time when one of my technicians tried charging me extra to do a Job for one of my customers. Tried to justify it to me saying he had to spend an extra 3 hours on the Job and run an extra 100 feet of cable.
A said to him, what about the Job you did the day before where the customer had Directv and all you had to do was swap the Dish, didn't use any new wire and was out of the customers home in 45 minutes. Do I get to pay you less money for that Job, since afterall you billed me for a complete install as if you had to run all new wire.
The point is that he didn't say anything to me after that, and dropped the issue.
The point im getting at is that its ok for the installer that you installed the pole and did half of his work for him, and now that you ask him to do something considered to be extra he is getting all pissy with you now wanting to charge extra.
The other issue was probably that he didn't like that you where telling him what to do, where as most Jobs the installer makes the determination where to run the wires and where he is going to mount the Dish. To be honest with you, I don't like it either when I get to a customers house and they already have the entire install planned out for me and have everything already figured out for me as to where im going to install the Dish and exactly how im going to run all the wire.
Now granted I probably would not have said anything on your installation if I was the installer, but it does irritate me and most installers when they go to do a Job they are under the impression that the customer is trying to create more work than is necessary