I bought my 2010 SHO non pp with 145,000 miles on it. It looked clean as a whistle when i went to look at it, and didn't show signs of abuse, so i took a gamble. It was only $11,000 on road.
It was fully loaded too, every single possible option right down to massaging seats and radar cruise control were optioned.
I was worried about the miles but the car runs very well.
I think that miles tells only some of the story, if the car is well looked after and has high miles it might be a steal. If you abuse a car for 50,000 miles then you may be paying for a problem you thought you wouldn't have.
IMO you can tell how a car has been treated by looking at things like the trim,paint, wheels (gutter rash etc), check the in dash AVG MPG and see how close it is to 20MPG (it probably hasnt been reset since the last owner drove it)
You can tell a thrashed/abused car by the way it looks.
Also - is there a service history log? If so even better.