At her favorite restaurant, Sami orders and enjoys the lobster special, which was listed at $30 on the menu. When the bill arrives, Sami tries to execute a clever ploy she learned about in her business law class: She writes a check to the restaurant for $20 and writes "full settlement" across the top. The waiter accepts the check without looking at it, and the restaurant manager later deposits it in the restaurant's bank account. Is this a liquidated or an unliquidated debt? Is Sami off the hook for the last $10?

NO It will pay the remaining 10 dollars later.

Explanation:

There are four requirement according to the Uniform Commercial Code:

You and the creditor disagree about the claim amount or haven't finalized it. The paid in "full statement" is easy to see. You pay the amount in good faith. The creditor cashes the check.

In this case the first and third criteria are not met. The amount is certain, easy to identify the cost of the service and both parties are informed of these amount.

Also, is important to notice Sami is not acting in good faith at all. Is doing this to exploit his knowledge over the waiter.

The fact the restaurant cashes the check do not avoid further claims on Sami the UCC (Uniform Commerical Code) gives about 90 days after cashing the check in favor of the creditor to change his mind and proceed with the collection of the full amount.

Most probably Sami will have to pay the ten dollars later or to find another restaurant.