This is actually a common business problem -- when the customer doesn't know how to tell a good product from a bad product, bad products slowly drive away the good ones, since if the customer is willing to pay a high price, the margins are better selling the bad product at that price, and if the customer refuses to pay a high price, then the low cost of the bad product makes it more competitive. :/

The best guard against it is education. The challenge is that if there is an easy "how to" guide for cast-iron kettles, it isn't something everybody knows about. (If anybody does know of one, let me know!) To my mind, there are two different ways to go about this.

You can start with the finished product; find a place that you trust to sell genuine and expensive Japanese-crafted cast-iron kettles, and give them a close look. See if you can tell what is different between them and the cheaper kettles. Those differences may be clues towards what makes quality. The downside is, of course, that the cheap kettles will do their best to disguise themselves. :)

The other way is to start with the materials. If you are the sort who enjoys learning the nitty-gritty of blacksmithing and metallurgy, you can find what to look for from the perspective of ironworking. (Or if you know someone like this whose opinion you trust, ask them for the short version.)

One shortcut that sometimes works is to find out who made the piece you are wondering about, not just who distributed it. If it was made under harsh labor conditions that prioritize speed, there may not be much quality control. Unfortunately, many distributors are quite secretive about which factories their pieces are made at, even though most factories won't sell single pieces directly to an end customer. Sometimes you can find out through the Bills of Lading, though, if you don't mind Googling for customs paperwork. Of course, stores that aren't feeling insecure might just tell you if you ask them. :)