To choose a coin dealer, evaluate the candidates based on their experience in the field, their financial stability, and their reputation among other collectors. In addition to this, confirm that the dealer is ethical and that he is equally attentive to all his clients. Make sure that you have a recourse in case some kind of dispute arises. It is ideal if the dealer is certified and is a member of official numismatists' associations.
The coin dealer's experience is most important if you are making serious investments in coins. An experienced professional should be able to evaluate the risks of an investment and the potential profit.
Most coins on the market are real, but sometimes fake ones turn up. If a coin dealer has a good financial situation, he is likely to still be in business in several years to provide a refund if the coin you bought turns out to be fake.
Professionals typically know more about each other than their customers know about them, so if a coin dealer has a bad reputation among his peers, it's probably not a good idea to work with him.
A good coin dealer is always looking for rare finds and good deals. However, an unethical dealer might offer you a price that is priced too low or too high to make extra profit for themselves. This is an important thing to consider when choosing a coin dealer, especially if you don't know a lot about coins.