Bad luck. It is always disappointing to find an item faulty and buying from a seller who is only starting out so with little feedback can be risky but I suspect that we may have a case of two genuine parties( buyer and seller) who are unnecessarily suspicious of each others' actions
Common belief is that the CPE2 should not be used without water and this is correct. However unless you ran it for quite some time I doubt if it has been ruined. Certainly the fault would have manifested itself within less than a minute - maybe in much less than a minute as the reverse turn occurs within a few seconds or not in your case so I don't think you have ruined it.
If you got the CPE2 for the end bid price as hown on e-bay then this is fairly good value, given that the solution suggested by others works and I see no reason why it won't. Did you get the other bits and pieces shown as well?
Hopefully this transaction will end satisfactorily.