Not to say that I'm qualified to distinguish well-written from not, since I'm a newbie in this area myself, but isn't the ability to do just that at least partially hindsight-related? It's hard to distinguish good from bad without the experience to back it up...

That being said, you can definitely tell when somebody's put effort into something they've written. The approach I'm taking is to both run it past more experienced heads once my "common sense" filter rejects the poorly written ones, as well as little mini-experiments to see if anything merits investigation on a larger scale.