I've used Provident Metals for both gold and silver. Physical gold, get whatever is selling at the lowest premium. They also sell "junk" silver eagles, which are marred or defaced (some were painted!).
https://www.providentmetals.com/
They buy and sell.
For "interesting" coins, I used
https://www.gainesvillecoins.com/
Also I also bought junk silver (mostly dimes). The "big bags" are almost always filled with crappy dimes. They sell the bags by denomination ($1000 = 10,000 dimes). Anything but dimes were a premium.