Quite aside from all the other ethical issues about purchasing ancient artefacts on the black market at bargain prices, there is also a high chance, that you might not get exactly what you thought you were paying for. Quite why people think that someone who would loot ancient sites is likely to be true to their word, in what they claim something is is another matter.
One also has to ask, how someone expected to pass off as legitimate, exact copies of works from a major museum.
BBC News 
3 April 2012 Last updated at 16:23
‘Ancient’ Greek statue found in sheep pen is fake
An “ancient” Greek statue found in a sheep pen north-west of Athens last week has now been deemed a fake.
At first, archaeologists at Greece’s Culture ministry thought the figure of a woman dated from the 6th century BC.
Now, a closer examination has found moulding marks and traces of bubbles which prove it is a copy, sources at the ministry told news agencies.
Two men were arrested last week for allegedly trying to sell the statue for half a million euros (£417,000).
They are currently awaiting trial on charges of looting antiquities.
The figure is 1.2m (4ft) tall and depicts an archaic maiden, but experts are now certain it is a cast rather than an original sculpture.
They say it is an identical copy of a statue found in the Acropolis in Athens, and not an item of “priceless historical value” as originally
Greek Reporter 
Ancient Greek Kore of…Industrial Origin
By Marianna Tsatsou on April 3, 2012 in New
Illegal traders in antiques, policemen, archaeologists, and all people connected to ancient items were looking forward to finding out if the Kore called “Peploforos,” which was found in a sheep cote in Attica, was ancient at all!
According to those who have the appropriate knowledge (that is, the archaeologists), this statue is a very good replica of the original one, displayed at the Akropolis Museum.
The illegal traders got arrested and the would-be “clients” felt really relieved. Not because they aren’t in handcuffs right now, as we would think, but due to the fact that they now know this Kore was not an original one. Had the traders not been arrested, they would have wasted 500,000 euros!
This price may seem pretty high for the average Greek, who owes money to his children’s teacher, to his butcher, and to the baker! But such a statue costs millions, and the buyers seemed to ignore this fact.
According to Professor Vassilis Lamprinoudakis, as well as to archaeologists and conservators, they realised from the very first moment that this “Peploforos” could not be real.
But the person who sculpted the fake statue did a great job. Its color, size and even its marks or missing pieces of the statue, are exactly similar to the original Kore. The latter was found at the Erechteum on the Acropolis. It is 1.20 metres tall and made of Parian marble. The traces of paint are still visible, although faded a little bit. This Kore was named after the red garment put on her waist, called “peplos” in Greek.
The last station of this new Kore’s “trip” will be the National Archaeological Museum in Athens, where everything that is confiscated goes.