TSR2:
I understand what you are saying, truly i do but unfortunately alot of people are not as accommodating as you appear to be.
Some flights, especially ones where there is generally alot of children can sometimes be impossible to move unless bribed and will also depend on what kind of pax you have on board.
Don't want to tarnish people with the same stick but there were occasions where i would have to physically tell people that they have to move in order to accomodate, almost upsetting one lot of pax to please another.
It's not the nicest position to be in so personally, and i know you don't really want to, either pre book or turn up mega mega early. The only way that you can really be sure. Turning up 2hrs before may be a little too late and depends on how many are already check in.
If your tour operator is Kiss Flights who are the main booking agent for Viking then you can pre book seats at £10pp return. One of the cheapest out there compared to other carriers.
Thanks