I'd have thought a nibble was something small enough not to make much of a visual difference to an appearance or be especially noticeable - certainly no more than a half-centimeter, and a chip is something that is larger and more clearly visible.
Then we have fleabites, which I assume are those tiny pinhead type of bits of damage... not sure if this helps at all Jayne.
Was it an eBay sale? If so, can you not do a Not as Described Report for it?
@Keith... it depends how big your potatoes are!