In google map for all the infoWindow the content is already binded to the markers, and whenever we open the infoWindow we get the binded content of marker on the infoWindow.
In google maps there is a listener for infoWindow that is domready, it is called each time the infoWindow is displayed. so we will bind the listener as
google.maps.event.addListener(infoWindow, 'domready', function() {
checkSelect(entityID); // EntityID here is the id of the user
});
so whenver a infoWindow is opened the function checkSelect will be called.
And the checkSelect function will check whether or not the ID passed is present in the hash. If it is present then that user is selected then just make the Select button disabled for the current infoWindow. I have created a dummy example. You can see that at http://jsfiddle.net/prabhat_rai/zpx7qfh5/