The above is an image of an authentic Flowing Hair Silver Dollar, Small Eagle Reverse, and it's one of the top counterfeited coins. It's important to study the coin series you collect or find images and authentic examples to make sure your coin isn't fake. Use this image and compare it to the two fake coins below.
It's not always easy to tell the difference, but often weighing a potential fake will solve the issue. However, many counterfeit coins do weigh the same as an authentic example. So studying the design is crucial and asking experts is a must.
The above is an image of a counterfeit 1795 Flowing Hair Silver Dollar, Small Eagle Reverse, and is not an obvious fake in appearance. The counterfeiter used the "wear" technique to obscure important details of the coins design.
Usually a coin like this must be weighed and often don't have the same thickness or even patina of an authentic Flowing Hair Dollar. The incorrect thickness should be obvious, but if not, study the lettering carefully. Most often the lettering and date digits will not have the same size shape or edges, and this is do to the counterfeit die loosing some details as it was created.
In the above image, compare the Y on both coins among the other letters and you will see that the fake's lettering is a little mushy. A seller will try to say it's because of the wear but don't buy it. The amount of wear on this coin would not cause the lettering to be misshapen.
The above is an image of a counterfeit 1794 Flowing Hair Silver Dollar, Small Eagle Reverse, and this coin looks too good to be authentic. The details of the hair is to pronounced and the eagle's breast feathers are the incorrect shape, and the relief in general is too high (meaning that this coin is struck in high relief and no Flowing Hair Dollars were struck in high relief).
I wouldn't be surprised if this fake was the same diameter, thickness and struck on a 90% silver planchet, but it's in the details that make it a counterfeit.
An example, in this condition, would be worth well over $500,000 and would not be found for sale cheaply. Just look and compare it to the authentic 1794 below.
The above 1794 is graded MS61 and is one of the finest known in grade and strike. It sold for $503,125 in 2009. So, please be careful buying any silver dollar because it can cost you. Plus, it's illegal to own any counterfeit or fake or copy, unless the word COPY is stamped into to coin and can be read noticeable.
Each silver dollar type above was only minted during these years as shown, but you also must take note of what mint mark was used on each year, and never buy a year that has a mint mark not used for that year. In example, a 1921-CC Morgan Dollar never existed nor does an 1872 Trade Dollar. So know your types, know your dates for each type, and know the mints that minted the coin date for each year.