There are particular coins and sources that one should avoid as one goes through his coin collecting hobby. The first and most obvious are dealers that peddle their wares on TV shopping channels. They usually offer so-called premium mints, which could be handsome commemorative coins that have little bullion value, if any. The problem with these sources is that their prices are extravagantly high, while the value of their products is shockingly low. Even if genuine coins from the U.S. Mint are offered, which they sometimes do, the prices are so staggeringly beyond the coins' normal price range. They typically do not offer anything rare, with most of their items being readily available from regular coin dealers.
Aggressive marketing companies such as Bradford Exchange and Franklin Mint are not to be trusted either. They do sometimes sell coins of genuine bullion, but beyond these, the coins hardly have any more value. And like those equally aggressive TV marketers, their selling prices are ridiculously high as well.
Next in line are those sets of coins usually found in magazines and TV shopping channels as well as swap meets. These are common or low-grade coins which are collected into a set of specific themes. To help them sell, they are usually packaged in a fancy and nice plastic holder or in any other premium packaging material. Just for their packaging, one can be seduced to shell out forty or fifty dollars for a coin set that is only valued at two or three dollars on the whole. What a rip-off.
These coins are usually marketed as having been minted during the Vietnam War, during the Second World War or otherwise may be commemorative celebrity coins or coins featuring cartoon characters. They are generally genuine, but in terms of value, they do not really appreciate significantly.
Also beware of coins being issued by the National Collectors Mint. This company is well known by its past advertisements that have been patently misleading. They state bullion values of their coins fraudulently, which are simply worthless in terms of collectability or financial investment. Even their name is quite misleading; they actually have no connection whatsoever with the United States Mint.
Finally, one would do well to avoid damaged coins. These are coins that have been modified or damaged in any way. Such damage includes painting, stickers, coloration, damage to the coin's form and shape, and other similar disfigurements. Serious coin collecting hobbyists or investors avoid such coins. Their only obvious value lies in their bullion value. In the coin collecting market and in terms of aesthetic value, however, their impurities degrade them.
If one is to really invest, it is best to look for that key date coin in its best possible grade. These are the best investments. If it cannot be afforded, the next possible thing is the more common coins in their finest possible grade. Good quality silver coins are great, as well as most nickels from the U.S. Proof sets are also a winner. In terms of obsolete coinages, one can safely consider silver half dollars featuring Kennedy, Franklin and Walking Liberty coins. One can also consider investing in bullion coins. This is one aspect of coin collecting.