The gain on that looks a bit low (I get ~108). But, you also don't know how the device is behaving as the Vce increases as ther amp output swings between the two rails. The +ve side spike almost loops like the device is 'snapping' to some kind of short circuit mode.
I earnestly recommend that you never ever buy parts off eBay - always stick to mainstream disti's like Mouser, Digikey, RS etc. You do pay more, but you know what you are getting.
Below is a circuit diagram - you should check all your quiescent DC voltage against this with no input signal.
If the voltages are all ok, try please try this:
1. Connect the PSU to the amp (especially the Zobel connections - do not leave these off. Make sure the wires to and from the amp module are tightly bundled together
2. Run the amp with no load and a 1kHz input signal and see if it swings up to the rails - if it does, I would suspect the driver gains are dropping off at higher currents load currents. Check the 0 Ohm jumpers - make sure they are 0 Ohms and have not been damaged and gone high R during assembly.
Come back and let us know what you have found (are both channels behaving like this?)
