There are many more repro's around than ever before, especially in ceramics, paintings and jewellery.. Many of these repro's are themselves old, like Staffordshire from the 1950's revival. They are worth about 1/3 of the value of a pre-1900 piece.
Because the sellers on EBay are a mixed bunch - of shops, professionals, semi-professionals and amateurs, ethics cannot be taken as given.
I have bought a few pieces that turned out to be repro's - but I never paid top dollar for one.
The rules are very simple:
.... YOU DON'T KNOW THE SELLER
......THERE IS SOME DOUBT IN YOUR INTERPRETATION OF THE WORDING IN THE DESCRIPTION
......THE SELLER CANNOT OFFER AN UNEQUIVOCAL ANSWER TO YOUR QUESTIONS OR DOESN'T KNOW
.......YOU LIKE THE PIECE ANYWAY
......THEN YOUR MAXIMUM BID SHOULD NOT EXCEED THE VALUE OF THE ITEM AS A REPRO.
If the seller has mislead you you can always have a dealer look at the item and open a dispute if it is phoney.