Well, for handmade clothing I look for:
Serging
Topstitching
Seams that don't have the thread showing (like too big of a stitch)
If it's something that is "worse" than my skill level, I wouldn't buy it. I might say "oh that's a cute skirt, but not serged. I could make one myself..." and put it on the list of things to do. No offense to the designer, but that's how I like it.
And the "perfect matching seams" thing? Nope. I like a little bit of wonk as apposed to mass-produced perfection. :D Clothing, the standards are tighter because otherwise a garment wouldn't fit right, but quilts? Love me some wonk. :D