contract-law
When purchasing with excess cash in a shop, is the sale completed when I pay, or only when I receive change
<p>I'm asking purely out of curiosity, and would be happy with answers relating to any jurisdiction(s).</p>

<p>As an example, Ben wants to buy a banana from Sam's shop. Bananas are priced at £0.50 each. Ben puts the banana on the counter and (a) hands Sam a £1 coin. Sam then puts the coin in the till and (b) gives Ben a 50 pence coin.</p>

<p><strong>Was the contract made and completed at point (a) or (b)? Or is the time of sale not legally defined so precisely?</strong></p>

<p>Presumably if it was not made until (b), then Ben might not be entitled to walk away with (or eat) the banana without waiting for change.</p>

<p>But if it was made at (a), then Ben might not be entitled to change his mind and get his £1 coin back if Sam was out of change and asked him to wait for five minutes.</p>

<h2>Neither</h2>

<p>The contract is <em>completed</em> when each party has totally fulfilled its obligations under the contract. In this case, it is when the purchaser has consumed or otherwise dealt with the banana to their satisfaction. The vendor has ongoing obligations under the contract until this happens. For example, obligations that the banana is of merchantable quality and fit for purpose. If the purchaser peels the banana and discovers that it is "off" or eats the banana and develops food poisoning then the vendor still has obligations and can be sued under the contract.</p>

<p>Yes, I realize that no one is going to sue anyone over a rotten banana but let's assume that "banana" is code for 54km of motorway construction and £1 is actually £1 billion.</p>

<h2>When is the contract <em>formed</em>?</h2>

<p>This is not a trivial determination and there are literally hundreds of thousands if not millions of lawsuits that have turned on this exact question. Once the contract is formed its binding on both parties; until then, either can walk away (subject to <a href="https://en.wikipedia.org/wiki/Estoppel" rel="noreferrer">estoppel</a>)</p>

<p>The traditional analysis involves <a href="https://en.wikipedia.org/wiki/Offer_and_acceptance" rel="noreferrer">offer and acceptance</a>.</p>

<p>In your banana scenario, the shop displaying "Banana's: 50p/each" (it's a fruit shop - they always have unnecessary apostrophes) is <strong>not</strong> an offer - it is an <a href="https://en.wikipedia.org/wiki/Invitation_to_treat" rel="noreferrer">invitation to treat</a>. An offer is made by Ben placing the banana on the counter and proffering the £1, it is accepted by Sam taking the £1. At this point, the sale is binding on both parties.</p>

<p>Ben has fulfilled all his obligations under the contract, Sam still has some. In addition to those discussed above, he owes Ben 50p. Strictly speaking, this is not an obligation under the contract but a debt due and payable.</p>

<h2>Consumer protection law</h2>

<p>The proceeding is a strict contract law interpretation - many jurisdictions have consumer protection legislation (and food safety laws for bananas) that impose additional protections and may change the contract law position.</p>

<blockquote>
  <p>Was the contract made and completed at point (a) or (b)? Or is the time of sale not legally defined so precisely?</p>
</blockquote>

<p>In the scenario and particular ramifications you outline, identifying a precise instant where a contract ensues would be pointless and/or inconsequential. That does not mean that your question is pointless, though. The possible developments mainly have an effect on Ben's entitlement to <em>void</em> the contract.</p>

<p>Ben satisfies his obligation as soon as he pays an amount no lower than what Sam asks for the banana. From that point forward, Ben is entitled to walk away with (or eat) the banana. In the event that Ben overpaid, Sam's pending obligation to return change does not hinder Ben's entitlement to the banana.</p>

<p>Ben has two options if Sam fails or refuses to return change:</p>

<ol>
<li><p>Void/rescind the contract (i.e., Ben changes his mind), thereby getting reimbursed. Obviously his consumption or deterioration of the banana would forfeit his ability to exercise this option.</p></li>
<li><p>Sue Sam for breach of contract, unjust enrichment, or --if Sam's deceitful intent is proved-- fraud.</p></li>
</ol>

<p>Option 1 is available because, in terms of the <a href="https://www.nylitigationfirm.com/files/restat.pdf" rel="nofollow noreferrer"><em>Restatement (Second) of Contracts</a> at § 151-153</em>, Ben's "<em>basic assumption on which the contract was made has a material effect on the agreed exchange of performances</em>". Here, Ben's <em>basic assumption</em> is premised on the price tag "50 pence". Ben, as "<em>the adversely affected party</em>" in the <em>actual</em> (versus agreed) exchange of performances, may void the contract.</p>

<p>Eating the banana despite knowing that Sam was out of change puts Ben in the position of <em>Bear[ing] the Risk of a Mistake</em>. See <em>Restatement at § 154</em>. That forfeits Ben's right to void the contract, but not his entitlement to receive change.</p>

<p>Common practice also reinforces Ben's entitlement to change his mind. This is contemplated in <em>Restatement at § 222</em> ("<em>Usage of Trade</em>"). Indeed, it is common and quite acceptable for a customer to desist from the purchase if the seller has no change. That is understood to <em>inconvenience</em> the customer because of the resulting delay. If Sam sought to force the purchase, his burden will be to prove that this instance is special and entails <em>questions of fact</em> in which he would prevail.</p>
