A commas market is not only SOL liquidity: its escrow holds real copies of the collectible that holders have deposited. Any of them can be taken out by anyone willing to pay what a copy is worth.

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How redemption works

1

Check the pool

The trade panel’s sell side shows how many copies the escrow currently holds. If it holds none, there is nothing to redeem yet; copies appear whenever someone pays with the collectible.
2

Redeem

You pay tokens equal in value to one copy at the current price, and the copy transfers to your wallet. The tokens you pay go back into the market’s item reserve, so total supply never changes.

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The math, concretely

Say the collectible’s live index is 0.44 SOL and the token trades at its fair value. Taking out a copy costs exactly 0.44 SOL worth of tokens. If the token trades below fair value, a copy costs more tokens (each token is worth less); if it trades above, fewer. You always exchange equal value at execution.
Redemptions are first-come. The escrow is a shared pool of copies, not per-depositor lockers: depositing a copy sells it to the market, and any holder can be the one who takes it out.
This two-way door: collectible in, tokens out; tokens in, collectible out: is what tethers the token to the real market. When the token is rich, depositing copies is the profitable move; when it is cheap, taking them out is. Either way the arbitrage pulls the price back toward the collectible. The full loop is walked through in Economics.