Below are some pictures of fake Bulgarian "uncleaned Roman" coins which were found end of 2003, early 2004 in batches of uncleaned coins sold by dealers all over the world.
Since then the fakers in Eastern Europe, notably Bulgaria are making extremely good fakes using a striking process and shifting them to western Europe using friends and family as mules, travelling unsearched and protected by the ridiculous, over-liberal, "we are all well-meaning brothers and sisters" EU laws, which means that when they arrive in e.g. Germany, France or England, their luggage is not searched - hence the increase of fakes now being sold from addresses in these countries - often with the seller knowing full well that they are fakes but enjoying huge profits from the sales. (One fake seller in Germany was raking in over 12,000 Euros a month selling fakes, until the police caught up with him).
Note that the images below are only a few samples of the old 2003-2004 fakes. Just about every type of common-ish bronze coin is now in circulation as a fake. Most fakes are those of Constantine I and II, Licinius I and II, Constans, Constantius I and II, Valens, Jovian, Septimius Severus.

If you are new to the wonderful world of Roman coin collecting, and are thinking of buying coins on ebay, please use common sense. Visit other websites such as the ones mentioned on the main page to compare the coins you are thinking of buying, with genuine ones.

Some visible giveaways of some (but not all) of these fakes are:

• The childish type of "artwork" especially of the bust
• The exaggerated "Roman nose" and the overly circular eye
• The size of the lettering is too large
• The crest of the helmet on VRBS ROMA coins is too far back
• The yellowish colour of the coin - they are made of copper and not of bronze
• The blobs of green (much of which flakes off when you run your nail over it) - it is a fake "patina" or artificially generated verdigris.
• Some coins seen to have been shaken in soot (black areas which stain your fingers and which wash off under running water).
• If you scratch some fake coins with a pin, it scratches very easily because copper is softer than bronze. The colour of the metal where you scratched is bright golden, not yellowish-brown as it would be with an genuine ancient bronze coin
• Most of the fakes coins have the same thickness all over the coin.
• Most seem to have one single area of "wear"
• Characteristics of the reverse of the fake coins are also a giveaway, for example
  • Victory's wings are simple lines
  • the lines of Victory's skirt are not parallel and they are "wobbly". Furthermore, Victory looks bored to tears, and there is no "action" in the illustration.
  • The palm which some Victories are holding look like a dumbell
  • soldiers on Fel Temps and Gloria Exercitus look as though they have been drawn by a 6-year old child
  • Banners and banner decorations are oversized.
  • Mintmarks are incomplete (many are just SMN without an officina letter).

• Check the "look" of the coin against a reliable website such as Wildwinds
• Ask the seller if it is genuine and whether he offers a refund if it turns out to be a fake
• Check the coin against reliable websites.
• Check the seller's name against the regularly updated Fake Sellers list on Forum Ancient Coins.
• If you see a fake coin on ebay, ricardo or yahoo auctions, write to the seller. It is illegal to sell fake coins in most countries without clearly describing them as such. If the seller refuses to stop the auction or change the description, write to the administrators of the auction site. Ebay do NOTHING - they are apparently more interested in their sales fees than protecting the innocent buyer - but if enough people write, maybe they will shift their backsides now and again and do something about it.
• Be wary of short-term (1-2 day) ebay sales. These are often a way for dishonest sellers to "grab the money and run".
• Barbaric imitations (usually struck in 4th century Britain or Gaul) are not classed as fakes ! These are usually recognizable by their peculiar-looking busts with a full eye, large noses and often garbled legends. Ones found in England often have a greenish-grey-blue tinge from the natural chemicals in the ground.
• Also not classed as fakes are the (usually Severan) AE versions of denarii, which were struck officially in bronze at military mints along the "Limes" border (along the Danube frontier). These military centres didn't keep much silver on hand for security reasons so struck bronze versions of denarii.
• Having said all that, some people collect fakes, so don't despair if you get one or two. And if you get a nice Fel Temp (fallen horseman type), I'd be happy to swap it with you for a couple of genuine coins :-)