If you read the various threads on this forum and on other places like SFI (
http://www.swordforum.com), you'll find numerous references to not only which actual products are good buys and usable, but you can learn various tells in marketing and in the products themselves which will help you identify them as being functional versus purely decorative.
The range of Usable swords goes from down in the $150 range with the Hanwei Practical Katana to well over $10,000 for a nice Japanese shinken. Does cost ALWAYS proportionally convey quality? No. However, if you hear someone spending $50 on a sword, you would have every right to be skeptical.
Normally things you can buy from conventional catalogs, you need to be very careful with, unless you're familiar with THAT particular brand or THAT particular sword. If it is identified as any of the 400-series stainless steels (440, 420 in various designations being most common), you may want to back away from it. Certain makers can do excellent stuff with stainless, but it is not common and should be considered more the exception rather than the rule.
Next, if you can *see* a noticeable secondary bevel on a sword, you may want to think twice. Granted, some quality swords have these, but if you are looking for a more-or-less traditionally styled sword, you will find that secondary bevels are usually not found. To illustrate what I mean by secondary bevel, imagine swords being stamped out of sheet metal in a factory with an "edge" approximately 1-2mm thick. Near the end of production, the actual sharp edge is ground on at a less acute angle, creating the "secondary" bevel that you find on the vast majority of knives.
If there are gems, elaborate carvings or overly gaudy metal (particularly brass) work all around the scabbard, odds are you won't find a good blade inside.
If you see a small nut or tassel plug at the very end of the handle, it is likely not something that will make you happy. While I don't doubt the possibility of swords with this construction being good, they did not exist in real Japanese swords, and the vast majority of ones sold with these details are often quite low quality (I've even destroyed a few myself).
There are other warning signs and stuff, but this is a good starting point for some.
I think if you want to get a feel for what constitutes a "good" sword, you should probably dig up some recommendations for your particular art, for your priorities in sword use (where you prefer your balance of "power" and "quickness" and so on), your price range, etc. Getting something recommended to you is a good way to start noticing a lot of the less tangible or describable qualities (you'll hear people tell you "good swords have distal taper, good swords balance nicely, good swords flex 11 billion degrees and return true..." I suggest you take those things with a grain of salt) that constitute "good" in a sword.
Hope that helps just a little.
