I guess that I go by how the fashions look on the models.
If the pants look way too tight on the slim-ish models, then I know I need to size up.
I'm the one who doesn't like items that look 'too tight', especially at the seam of 'buttom' area.
Too uncomfortable to wear in the cr*tch area, etc.
'More or less', 'Right or wrong', 'In general', and 'Just thinking out loud ' (as usual).