What's the best way to go about scaling things?

I was playing around with the engine over the last few days as a newbie should and having fun. Drop house here, castle there, barrel there. Wheee...

Well, I figured I'd mix things up so I increased the scale of a few of the houses to add some different sizes. Then I run into the house and find out the fireplace is taller than my player :)

Anyway, to the point of my post. This got me thinking. Particularly for those of us that are getting models from other sources, is there an easy way to keep everything scaled correctly in relation to one another? Or do you need to rescale each object as you drop it into the game?