While it's not uncommon for certain rare coins to have significant value, the claim of a single Bicentennial Quarter being worth nearly $350,000 USD seems quite extraordinary.
Bicentennial Quarters, minted in 1976 to commemorate the United States' 200th anniversary, are not typically considered among the rarest or most valuable coins.
However, there are certain varieties or errors within the Bicentennial Quarter series that can be valuable to collectors.
For example, coins with certain minting errors, high grades (such as Proof or Mint State), or unique characteristics can fetch higher prices at auctions or in private sales.
As for six more Bicentennial Quarters worth over $5,000 each, this could be possible if they are rare varieties, in exceptional condition, or have historical significance.
It's essential to have coins appraised by reputable numismatic experts to determine their true value accurately.
Additionally, factors such as rarity, condition, demand, and market trends all play a role in determining a coin's value.