How to tell a good tailor from a bad one?

So I'm looking to get another suit custom-made here in Korea. How do you tell a good tailor from a bad one? I've been to several and seen their handiwork and working premises, and about the only constant relationship between quality and price is that the less expensive you get, the more machines involved. Fabric's practically the same, and everyone says they're the best in the area. I'm wondering, if I got a decent suit for a certain price, and someone else asks for a couple of hundred dollars more than that price, where my money's going to go.

Thanks for the advice, guys. I'll be sure to tell the salesman measuring my body all the details. I know he's a salesman because he told me the tailor was busy working upstairs. I saw the drafting board that they presumably use for making my individual pattern, so there's a good chance that they aren't simply made-to-measure. I sat down with the salesman and discussed things like material, buttons, and stitching. The example he showed me was a pretty nice two-piece two-button suit made of navy blue worsted wool (with pinstripes.) The lapels were stitched and seemed to roll very nicely. The detailing, on the other hand, left something to be considered, and I have a feeling that the example he showed me was for a client that was willing to pay a bargain price and no higher. He did have real horn buttons, and that's a big plus. This one other tailor I went to said that it was very hard to find horn buttons here in Seoul. I guess he wasn't looking hard enough, or in the right places. He's also able to make suits out of Loro Piana and the like, but I'm opting for far less expensive, and quite nice in their own right, domestic wools. I went through two tailors before him. One doesn't do buttonholes very nicely, and the other did some fusing I didn't appreciate (the dual-vented jacket's vents; this causes them to curl outwards with wear.) I'm going to hit the department stores to see if I can't find something off the rack that offers the style and cut I'm looking for. Things should be relatively cheap now, with the seasonal sale going on (and the fact that the economy here is going south makes things all the cheaper.)