OK, here's my thinking:
This coin was - almost
certainly - holed very soon after it reached circulation. 160 years ago, someone wore this coin around their neck. Any wear the coin shows, was earned against someone's breast. A Civil War soldier? His sweetheart?
A little flesh for the story: By 1853, silver had reached the point where it was worth more than the face value of the coinage made from it. Silver was being hoarded as a result. That heaped a bunch of the daily monetary workload on the Gold Dollar, and in response in 1853 the Mint struck over 4 million of them, by far the largest single mintage of the entire Gold Dollar series. Gold - resulting from the California rush as well as continuing availability in the Southeast - was plentiful.
In further response to the silver weight/hoarding crisis, the Mint (Congress) lessened the silver content of its' coinage (except the Dollar) and minted a bazillion silver coins in 1853 at the new weight. End of problem with circulating coinage, and between the two major moves, a pretty good reason why the (relatively) few (855,000) 1854 Dollars were not only minted but available to become good luck charms around one's neck.
As a gift, it needs to be given with a chain upon which to wear it, to a person who can cherish the near-certain provenance it carries by wearing it for the same purpose. If this is an appropriate scenario to you, I see no reason to doubt the authenticity of either the coin or the seller. All the same I can't assign a physical value too much over $100 for the coin and then you still have to consider the chain.
That part's on you.
