The Romans minted coins using dies and hammering by hand. It is normal for the coins not to be perfectly round, thin, and for some of the image to be missing or off center. Chips are also pretty common. The coins are very old and have been through a lot.
When buying uncleaned coins you should expect them to be dirty. Understand that the finder obviously searchs the coins and trys to identify the higher value coins. Some coins may be totally covered in dirt but many will show some clue as to what it is (A low value bronze coin). Very few silver or gold coins make it past the initial sorting at the point of discovery. The basic fact is bronze roman coins are very common and the finder does not have any interest in restoring them. They sell the low value bronze coins to a wholesaler in bulk and they find their way to the U.S.A. and other markets.
Some dealers clean the coins and then send you their rejects. A cleaned coin will be showing metal and/or have no real dirt stuck on it! If the coin is mearly dusty it is also possible that it is cleaned. If you soak your coins in hot water and it doesn't get dirty then they have been rinsed. If the coin is cleaned (showing metal and/or has no real dirt stuck on it) or obvious junk (before cleaning) you are getting someone's cleaned or partially cleaned rejects. Some of the coins you receive will turn out poorly after cleaning. You should not expect them all to turn out poorly and you should not be able to tell before cleaning which coins will not have any detail (known as a slug).
The basic theme here is to keep in mind that roman coins come in many sizes and shapes. Each coin is unique. The quality of the cleaned coin will vary as they were in circulation before they were buried. The coins are very old, interesting, and have many stories to tell.
IF YOU ARE LOOKING FOR TREASURE STAY AWAY from uncleaned coins! It is unlikely that you would be able to resell them as a whole for more than you paid. Buy uncleaned coins or any old coins for fun and the history of them.