When somebody becomes concerned in challenge coins they look for places and people who will be able to sell, and in some cases advise them about, coins. With all of this facts they can tell you the best methods for cleaning coins without losing the diverse characterizing marks. The way you can make a profit from collecting coins is if they are rare or hard to find and old coins are your best bet because if you choose state quarters, they are all too recent and easy to locate. Collecting state station is a fun hobby, but they probably would not ever make you any real money because they are very common. Use an online auction to have access to thousands of coins from all across the world and you might be able to buy a very old coin or one that is from the 19th century. The grading of coins that is browbeaten will be looked into as well before the coin dealers agree to purchase any coins. Coins that are rare often times will be dirty to some degree and because of our human nature we will want them to shine and this has been a big mistake for many, because the coin loses its authenticity after the cleaning.   For example you will find coin dealers who stock civil war coins or colonial coins and there will also be coin dealers who have dozens of experience in dealing with foreign coins.