cheap cables have a higher resistance, causing a higher voltage drop when current goes through.
Your mobile will spot the voltage drop and limit the current.
You can but these little voltage/current meters to put inline of USB, get your good charger and mobile, and measure the current for each cable. Throw the bad ones in the garbage.
It is really hard to spot bad cables other that doing the above measuring. For example, on DX you can have very good ones and very bad ones, in the same price range.