After you have been selling for years you know who is buying and at what price.
1) For newbies it is best to walk around and sell to dealers. Buy prices are 10-40% below ebay sold prices, common stuff and items below $500/unit 40% below ebay, rare stuff or or items above $1500 10% below ebay. I pre-arrange almost all my transactions so I don't have to spend more than a day at the show. For example, you send me a picture of all your coins and we work out a price and then at the show we do the transaction with both sides committed to the transaction. The only challenge is when the market is hot and dealers want to buy, collectors hold on tight to their coins because they don't want to miss out on higher price so they miss the opportunity to sell at near market prices, when the market is cold then collectors become motivated to sell and at those times dealers are offering 20-40% below the market prices because they are scared to catch a falling knife. The secret is to sell when the market wants the coins and buy when the market doesn't want you coins.
2) You can also get a table, but the cost is $1000, plus three nights of hotel. It is almost impossible to pay off the table fee by selling for a premium compared to what dealers offer you in option 1). If you have got $20,000 worth of coins that you think you can easily sell, then having a table maybe ok. The real reason to have a table is to buy, not sell. In recent years for MCC almost all transactions are pre-arranged so opportunity to buy is very limited unless the market is really cold.
3) Ebay is often the best venue for new sellers, ebay + paypal fee is 10% all-in, which is comparable to what dealers will offer you on rare stuff, but cheap for the common stuff. The best part you will learn what the market really thinks about your coins because you will be selling directly to collectors.
Regardless which option you decide to pursue to sell your coins, the most important thing is to do your research. There are a lot of free resources to help you decide what is reasonable price for your coins, view sold transactions.
6) NGC price guide
7) PCGS price guide
The above sources account for 85% of all PUBLIC market transactions for MCC so they should give a reasonable view of the market. However, keep in mind 95-98% of the market transactions are NON-PUBLIC so the price that you might get could be different from what your research suggest, simply because the PUBLIC market is not representative of what PRIVATE market is transacting at. This often happens when the market is very hot or very cold. During these times almost everything is sold privately and public transactions are often lagging the market by months to quarters. This is why I put so little value in price guides and even the above sources when the market is very hot or cold, which is when most of the opportunities exist.