Sorry guys but mad_jock has a point there.
Certainly as cabin crew it can be difficult when we do have to enforce something. When it comes to seating it has to be an exceptional case before crew have to make the decision that seating needs to be changed. Certainly in 9 years I've never had to do that. Generally you can appeal to people's better nature. If you have to enforce it then there is I usually a good reason and that reason should be fully explained to those effected. However, that decision will have been made and if it's for a justifiable reason it is not up for negotiation. That is where the problem lies. Passengers often don't see or appreciate the 'official' role of cabin crew and so if things have gone wrong and the crew has to ask/tell them to do something then they regard it as bad customer service on the part of the crew member....even if the airline is to blame.
I'm glad that the rule on electronics had changed as you could get some nasty retorts for simply and politely asking people to switch their device off. A lot of passengers often don't like it when crew have to ask them to do things in order to adhere to SOP's. Why? Because they only see and appreciate the customer service side of things.
Of course, there will be rare occasions that Hitler like crew will be on board your flight but there are also rare occasions where passengers will be difficult, will argue the toss and those are the times where you have to remain polite but also be robust. That is the point I think mad_jock is trying to make.