Dealers generally have the financial resources to buy all of your collection at once. Items not needed for the dealer's own stock can be quickly traded to other dealers.

Sale to recognized, established dealers is generally more private and secure than advertising your coins to the public, or even at a coin club meeting.

In almost all cases, you will only receive a wholesale price for your coins.

The prices offered by different dealers for the same coins may vary widely because of supply/demand (market) factors, dealer knowledge of the material, and the dealers' business practices and level of honesty.

As noted above, dealers often resell to other dealers at a markup, so there could be several "middlemen," reducing your proceeds, especially of you don't select the right dealer.

It's very important that you spend some effort finding the right dealer. It's usually better to sell to a dealer who regularly handles the type of coins (e.g., U.S. or foreign) that you have for sale.

Consider asking for recommendations from experienced collectors, for example at a coin club meeting.

Meeting dealers at a coin show may be better than going to a coin shop because you have access to many dealers instead of only one at a time. (However, don't expect dealers at a show to quickly appraise a large group of coins, or to buy a large hoard of coins that they have to carry out of the show. You'll probably have to make special arrangements, and may have to pay an appraisal fee if you don't sell to that dealer.)

Consider having valuable coins certified ("slabbed") in advance to reduce grading disputes.

Be aware that dealers are not completely immune from cash flow problems, bad checks, etc. Use great care in selecting a dealer for selling entire collections or high-value items.