How do I know if my coins are valuable?

Most people that receive or inherit a coin collection have no idea what they are worth.  If fact, most are not able to identify the coin, the mint mark, and the condition.  Coins can be tricky.  One of the more common coins that we see are older silver dollars.  Although the coin collecting heyday has come and gone, there are some coins that have maintained pretty good vale, and the silver dollar is one of them.  I am specifically referring to the Morgan silver dollar.  The Morgan dollar is the most collected coin in the world, because you can buy them fairly cheap, and for the rarest of dates and mints, you can easily exceed a million dollars.  Keep in mind that silver dollars were currency back in the day, so using a silver dollar to buy something was the same as using a paper dollars.  It's always good to get some help when evaluating a coin collection.  We live in an information age, with Google at our finger tips 24/7, but what if your not sure how to even identify the coin that you are looking at?  The nuance with coins is almost endless.  Google can end up leading you down the wrong trail.  I often hear from clients that they started trying to research their coins, but quickly realized that you have to have a certain knowledge base to even look up the right coin!
It's pretty simple, coins have value based on their rarity or based on the type of metal that the coin is made from.  Gold coins can be quite valuable without any sort of rarities.  In other words the gold is going to have value based on the gold market and how much gold is in that particular coin.  Again, the combo of date, mint, and condition is used to determine the overall rarity.  One of the common misconceptions is that if a coin is old, it must be valuable, but not so.
Along with silver dollars, we see a ton of old quarters, dime and half dollars.  Keep in mind that all quarters, dime and halves from 1964 and earlier have 90% silver.  Keeping in mind that the us mint made these coin to circulate, meaning that they jingled around many a pock and cash register.  The vast majority of those types of coins are not rare and have been heavily circulated.  But they are still made of silver and therefore have considerable value in quantity.
I am always amazed at peoples comments when I first meet them to evaluate their collection.  I hear things like, "I don't know if I should just take these coins to the bank and cash them in."  Those folks almost always fall out of their chair when I tell them the value, and again they really add up!  Even though coin collecting is in it's dying quivers, the metal is trading close to all time highs.  Gold and silver are valuable based on supply and demand.  There just isn't that much gold and silver, therefore it will maintain it's value.
One of the reasons you want to work with a coin expert verses a "cash for gold", is to identify the rarity.  I once had a client who initially took 2 older gold coins to a cash for gold shop.  He was under melt value for each coin($1500 each).  Within 30 seconds of him walking into my office, I know those coins were considerably more valuable that the melt value.  He ended up selling those 2 coins to us and we paid a little over $23,000 for both coins!  So again, it's definitely a good idea to work with people that have a expertise in the things you have.  I always ask a lot of questions before I meet with someone who has a collection to sell.  I want to make sure I am the right fit for the types of coins a person has.
You always want to error on the side of having more information about your coins, prior to selling.  Our first appointment with potential clients are always intended to educate people on what they have.  I look forward to seeing your coin collection!