My Sis Was Told This Was A Counterfeit, By A Coin Shop, But Can Anyone Help (1804 Dollar)

Unfortunately this coin is 100% fake there were only 20 of the 1804 dollars struck & is considered one of the rarest US coins ever. I believe there to only be a plain / lettered edge, so reeds are a dead giveaway that it is counterfeit. Also the overall appearance of the coin screams fake.
Edit - Not to mention every 1804 dollar was struck as a proof.

The overall strike looks mushy, lots of weakness.. Overall look appears wrong.. Also all of the 1804 dollars were struck as proofs.

The US mint didn't start using collar dies in the minting process until the late 1820s or early 1830s, so any coin that has a reeded edge (which is created by a collar die) is 100% a modern fake.

Also, wring forum. This is the modern error and variety coins page.

Pretty awful, even for a fake.

I thought it was in pretty good shape for a 215 yr old coin, just comparing to my coins that are from just 100 yrs ago

On a real one the denomination would be stamped on the edge. Instead of reeding it would be stamped "Hundred Cents One Dollar or Unit" on the edge. This was common amongst early coinage. PCGS has some nice photos of the 1804 draped bust dollar.

Many series (not just the USA) may not have had a denomination as a part of the obverse / reverse design because the size of the coin and weight made its denomination self evident. Especially with silver / gold coins where the weight of the metal mattered in its face value and as a result a transaction using coins from multiple issuers wasn't uncommon. For instance, in the early 1800s a lowly minted US silver dollar from its formative years and a commonly found Spanish Colonial 8R might be rather interchangeable as long as the rough weight of silver was the same. US Trade dollars came around decades later as the US tried to hold their place with the international silver trade market (especially around the Pacific) even though issues at home like the Morgans actually decreased in silver content. Notably, Chinese merchants therefore preferred other countries' "silver dollar" equivalents that kept the old standard up.

I lived in China for a couple years and would come across the 1804 copies rather frequently wandering around the markets. What you are showing us is exactly what the Chinese stuff looks like.

I'm imagining this came into one of your grandfather's banks in a roll or bag of silver dollars and got intercepted there. A fun pickup for a pocket piece, as long as no one tries to represent it as real in attempting to sell it.