The question of working on Shabbat seems so easy to answer one would be ashamed to ask. Of course it is forbidden... But...the world is a complicated place and thus things gets complicated as well.
The question is as follows. We have a synagogue with no hazan, old one passed away. When we required a hazan to come do the service on Shabbat. He stated that he wanted money in order to come. Is that not work ? We asked, and his answer, He is not working, he is a talmid showing us what he learned and practiced all week, and we in return pay him to continue the work and the learning cycle.
But as it was a small synagogue, and perhaps to prove a point it came to pass that we ran out of money, and so, the hazan refused to come when he was not paid. Call it what you will, but isn't that the explicit definition of work? to do one's request in exchange of wages.
Another good example we ran into was once we secured a hazan, he would be offered more money to do the high holidays in another synagogue, and thus, he would ask us to match or beat the amount in order to be here or he goes elsewhere.
What is the position on these?