Coin Appraisals
The Professional Numismatists’ Guild is very stern about its members, so look for a dealer that belongs to the Guild.
At the library, check out books concerned on coin collecting. They can help give you an idea on how common your particular coin is and an idea on its value and worth.
Try to get an understanding of the grading system. Some coin f=grades are Uncirculated, Proof, Mint, Fine, Very Fine, Extremely Fine, Good, and Very Good. Some people use other grading systems for their coins. If you keep a graded coin that you bought protected, it should stay the same grade. This helps when you are ready to sell.
Get an appraisal from a coin dealer for your coin. Remember that an appraisal costs you, so asked if the coin is worth getting an appraisal.
Study coins that are like yours in coin magazines to give you an idea on what price you might expect.
Since coin professionals are ordinary people like us who can furthermore make errors, you might want to have a few coin appraisals completed. With so many professionals you should find information which tallies, and ones that you can see eye to eye on. From this information the choice of whether to sell a coin collection or increase the different coins can be made.