An interesting item.
Let us for the moment assume it is a fake cancel over an erased specimen overprint........
Certainly the bar immediately above the '466' could be hiding an erased Specimen type 9. These specimens are handstamped rather than printed and it is quite normal for the specimen overprint to slope at the same angle as the bars in the numeral. This would allow the numeral to hide the specimen completely as far as the scan shows. It would be nice to have the actual item to check if this is the case. However without access to the item, the scan does not confirm it either way.
The general characteristics show that the item is a blued paper example, SG133, (rather than SG137 white paper). The 1883 cancel is consistent with this. That said, specimen type 9 on blued is the most common specimen type so the most likely candidate for addition of forged cancels. They were dirt cheap 20 or more years ago and are often found without gum. A used £5 on blued however has always been pricey hence the temptation to convert one to the other.
Let us continue to assume it is a forged cancel over a specimen:-
As the forger, having added the 466 cancel to an erased specimen, you now have a perfectly reasonable fine used £5 on blued - certainly good enough to fool most people. You have already created a very marketable entity compared to a relatively cheap no gum type 9 on blued specimen. If that is the case, why bother to add the additional Cavan cds when the Liverpool numeral would already suffice?
A Cavan receiver used in this way is somewhat unusual and is more likely to raise questions than a simple 466 numeral on its own. If that is the case, why forge the cds too? You might argue it was to date it in the blued period but surely Cavan is rather less likely than Dublin?
Is it genuine use?
Why might a Cavan receiver be on the stamp? If the parcel was a sack, it would probably have an address label tied on bearing the £5 (plus maybe other stamps) and the address. Indeed, as already suggested by chavander, there might have been no other place for the Cavan receiver to go - you can't cancel a sack! That all leads to it being plausibly genuine postal use.
I do not have a wealth of 466 cancels from that period to check against and even fewer (that is - zero) for Cavan. For the moment I decline to comment on whether they are 'ZINCO' or real cancels without further research.
Is it accounting use? I have not studied the relationship between Cavan and Liverpool. Is it reasonable to expect there to have been such a tie at that time that might involve a £5 orange? If there was such a relationship, should we not expect a lot more Irish cancels, in particular Dublin, than there appear to be? Maybe an Irish specialist might be able to provide some light on this?
It would be very interesting to have the postal rate tables for 1883. What type of package from Liverpool to Cavan would need a £5? Was it even possible?
If the ebay vendor withdrew it, maybe he has more information on it. I tend not to follow ebay so didn't see it, nor know the vendor ID. Does anyone know who it was?
Postal use of the £5 may exist, but is rare. Maybe this is an example, but without access to the item and further research, I cannot draw a firm conclusion.