Hi , that they are figure and not hockey or inline . Also that the blades are the correct size for the boot . That there is enough blade area left for subsequent sharpening and that they are not rusty. That the blades have been alighned properly when nailed to the boot. Also that the boot itself is not too worn , it should be able to support the whole foot and ankle .Of course , that the size is right too .
There are a vast amount of boots and blades out there , be sure of the new price of the skates so you know if you are paying fairly for the ebay ones. The boots have a wide price range , as do the blades , which also vary depending on what skating you are doing , eg : figures , jumps and general figure skating , and dance . :-) x