You can't
But there's some tips that make you notice the scale is wrong
For example the depth of field, if you got un-natural depth of field its because of the scale
Let's say you load a house, and you get depth of field like if it was a 1cm house
Or you can check with the AO distance, small objects are covered with AO while big scene you see some areas without AO
But the better way of checking the scale is exporting with correct scale in Sketchup