As long as they are upfront how their system works
They’re not. These are their instructions:
After purchasing the coin(s) from the US Mint, email Operations@PinehurstCoins.com to confirm the sale of the coin(s) to Pinehurst Coins.
We will reply to your email with a Purchase Order.
Absolute statements. No hedge. They don’t add “we may let you know hours later that we rejected your email because we filled our quota before you sent it”
If you don't like that you can either find a buyer who will commit beforehand (who will usually pay you less)
Actually the buyers here usually pay more ime, and they commit on the spot. Win win!