Coin USA specializes in rare and unique currency from the United States. They can grade a coin and put a value on what it is worth. Coins graded the highest are worth the most.
There are many gold dealers that specialize in gold coins for sale. If someone is looking for a gold coin at a good price you can look on auction sites such as eBay or a reputable dealer such as Midas Resources.
The word "specialise" is the British English spelling of "specialize" (US spelling).
A two cent US coin is larger in size than a ten cent US coin.
Sacagawea is on the US $1 coin.
They never have. If your coin has a hole and is a US coin then someone drilled it in. It was not done at a US mint.
The first US dollar coin was made in 1794.
You are probably thinking of an "error coin". This coin is any coin which does not meet the standards of the US Mint or has a flaw in its design or manufacture.
Harriet Tubman has never been on a US Mint Coin.
...Of what US coin? There have been several US coins intended for circulation ranging from half a cent to $20.
The US spelling is "specialize" (UK is specialise).
Take it to a coin shop. They will tell you if it is real or not.
Please be more specific which coin?