If I do get a look at a movement I'm not generally trying to guess whether it needs a service. More just to see if there is something grossly wrong with it or if the original movement has been swapped out. For example, I believe we've all seen automatic movements with missing auto-winding modules; that's a nasty surprise.

 

Phew......quite a disparate range of opinion and advice!
I guess what I'll take away from this is:

It is probably unwise to press for movement shots, as caseback removal is best carried out by a professional / watchmaker, and doing so could contaminate the movment / dial.
'buy the seller' x several
And of course that old adage, useful with any aspect of life...if in doubt, DON'T. (I do, though, seem to abuse this advice, regularly)

Thank you folks, as ever.

 

Some watches are really difficult to open by not an experimented person. For the rest i think a picture with the movement it's reasonable.