(Leura, NSW, Australia)
Some sellers at my local market have a range of swords under $50 AUS. How can I tell if these are any good?
Swords sold cheaply in a local market are usually only good for decorative display, not actual use. If this is what you want it for, go ahead and find the best looking one you can. Then hang it on your wall and enjoy it.
Don't use a decorative sword for swinging about and don't try to cut with it even if it is sharp. Most of these swords have a thin rod welded on under the handle instead of a strong tang. If you wave them about or hit anything with them, they are likely to break or at least bend. If a decorative sword is sharp, it can cut you or someone else when it breaks.
Real swords are tempered with heat to make them strong. They have a full tang and are made of strong steel such as high carbon. Ask the market seller about the sword in those terms and if they don't understand or can't give a satisfactory answer, it's almost certainly not a high quality sword. Save your money and buy something like this, if you want a functional sword http://www.chinese-swords-guide.com/Real-swords.html