As a collector of historical weapons, I've been through the process of trial and error. As a newbie on this particular area, I just bought whatever was the bang for the buck, shooing away legit swords for sword like objects. 440 steel was partner and rat tail tangs were my buddies; however, once I tried to swordfight with a friend of mine (caution; both swords and slo's are not meant for swordfighting), and after a hard blow my "katana" became three pieces as the handle remained in my hand, the tsuba went flying, and thankfully the blade just fell into the ground.  I reinforced the rat tang, and continued with the (stupid) exercise, until it broke again in the same fashion. Then I came to wonder why this swords were so brittle and weak, while a real katana was supposed to be very durable and strong. Along the way I began reading and learning about the tools of the trade in sword making revealing the following:

-any kind of stainless steel (420, 440c, etc) is ok for knives but too brittle for swords so stay away from stainless steel "japanese swords"             -the most basic of japanese styled swords (I'll explain that later) needs a full tang and must be made of carbon steel (1045 or higher)                    -a legit japanese styled sword is handforged and heat tempered even in its cheapest incarnation; machine made blades are unbalanced and tend to have ugly tips                                                                                                                                                                                                      -as a matter of fact you get what you pay for; don't expect a handmade, practical sword that costs you $9.99 with a $29.99 s/h cost (the only place i've seen these prices for a true sword is in razorsharpkatana on some auctions that start @ .99 cents)                                                        -beware of the Chinese antique seller who will rip you off with an cheap, artificially rusted and aged "japanese sword"  for .99 cents and charge you $100 in s/h costs                                                                                                                                                                                          -As such there are very few katanas for sale on eBay. For a sword to be called a katana it must be manufactured in Japan, and strict laws there hamper mass production of this swords. Any other katana resembling sword is called "japanese sword" or "japanese styled sword", regardless  of quality                                                                                                                                                                                                                                                                                                                                                                                                                        

Hope this guide gives you a few pointers when you get to buy sword on eBay. This is a very basic guide, but will provide people who are new in this some knowledge before commiting mistakes. SLO's are not necessary bad; if you want a fancy-looking piece hanged on your wall, it is more than acceptable, that is their intended use (hang on the wall or stay on the stand). Also keep in mind mineral oil treatment every two months will keep your sword in good shape (be sure to clean it after use). Japanese style swords are used for myriad purposes EXCEPT for parrying with other Japanese styled swords and using it as gardening tool