If you're buying something online, you know what might help? A digital 3D model file, to scale. That way, if you have questions about the dimensions of the object, you can measure it any way you like, inside the computer, as if you had the physical item with you, more or less. Or if you prefer physical objects to check, say, whether a particular toaster will sit on your kitchen bench easily (and you have access to a 3D printer) you could print out a model to test the fit in real space. I think this might easily be a feature of online shopping in the future, at least for some items.
Mokalus of Borg
PS - Obviously it wouldn't work for clothes.
PPS - And a rough paper cutout model would be more accessible for most people.