It is your lucky day - that crate of wine you bought online arrives at the door, but the supplier has made a mistake and two more come with it for free.
Three cheers for the price of one.
Before you invite friends over for an unexpected party, there is the small matter of whether you are entitled to drink those extra bottles.
The answer is no. You should contact the seller asking them to collect the extra crates. In fact, a trader can take court action if you refuse to return the goods after it has asked for them back.
Many thousands of consumers have found themselves in this situation, judging by cases seen by consumer complaints advisers.
Examples from James Walker, founder of independent consumer rights website Resolver, include duplications on orders of alcohol, mobile phones, and even a £500 kite. At times, errors occurred after the original order never turned up.
Helen Dewdney, author of The Complaining Cow blog and a book about how to complain, said her thoughts on the subject became the second most read post on her blog.
"Many people receive items that they did not request. However, most of the time they are not unsolicited goods," she says.
"Well over a hundred comments [on the blog], and only one was truly about unsolicited goods."
The distinction here is important. For example, an item that should have gone to a neighbour, but the house number on the package is wrong, or a mistaken duplicate order are not unsolicited.
You can only keep hold of an item if it is addressed to you, there has been no previous contact with the company, and it arrives out of the blue. This is a genuine unsolicited item and is usually used as a marketing tactic, explains Citizens Advice.
There are various rules regarding goods and services that arrive for free, or that a company fails to charge for. Hardly any of these regulations work in favour of consumers.
If a customer enters into a contract but a company fails to take any payment, then the item or service still needs to be paid for.
Similarly, if customers at a restaurant realise that something is missing from their bill, they should point it out to a member of staff. Intending not to pay for any item that has been received can be viewed as fraud, says Citizens Advice. In summary, there is no such thing as a free lunch.
Many people would argue that there is a moral obligation to pay for things that have been consumed. Others say that if restaurant staff make an error on the bill, then it is their fault that the full amount is not paid.
Those lines become a little more blurred if the diners only realise on the bus home that they were never charged for their dessert.
Free and easy
The growth of online shopping means that deliveries have increased in number, and so too have mistakes.
Items arriving in the mail is the one area where there might be some luck for consumers - even if they have relatively little to rely on in law.
It is extremely rare for genuine unsolicited items to be delivered to your door. This is when something arrives completely out of the blue, is addressed to you, and is something you did not order or ask for.
It does happen, but often it is a marketing gimmick with an item of very low value. Whatever the reason, the Consumer Contracts Regulations of 2013 mean you can keep the freebie.
Even so, with an item of value it is worth contacting the trader to check. Citizens Advice has a template letter pointing out that the trader can collect the item at its expense in the next 14 days "but after this time I will treat the goods as my own".
Unsolicited goods - in other words, freebies - do not include items sent by mistake, such as the wine crates example from earlier.
This is also true of refunded items that are faulty and waiting for collection, items meant for someone else, items sent in addition to an order, or replacement orders that have not been paid for.
In these cases, anyone who wants to keep these items will have to pay for them.
Otherwise, it is up to you to contact the trader to tell them to come and collect these goods. You should not be expected to pay for postage and packaging if sending them back.
Honesty was the best policy for Robert Quinn who, when an engineering student in 2014, was sent 46 items worth £3,600 - including a 3D TV worth £889, tablets, a games console and a leaf blower - owing to a mistake by Amazon.
The items were in fact returns, incorrectly sent to his home in Bromley, but after contacting Amazon, the company allowed him to keep them. He sold some off for charity, although his mum got the leaf blower.
The temptation for anyone in this situation, or one somewhat less dramatic, is to stay quiet and keep the items.
Whatever your views morally, the law clearly favours the supplier in this situation.
Craig McAdam, principal lawyer within Dispute Resolution at Slater and Gordon lawyers in Manchester, says that under criminal law this could be regarded as theft - defined as dishonestly appropriating property belonging to another with the intention of permanently depriving them of it.
A charge of theft could indefinitely hang over anyone who chooses to keep something that is not theirs.
In civil law, the company could seek to recover the goods or monetary value when somebody keeps an item not intended for them.
Under these rules, the trader has six years to chase the unpaid debt from the time the debt arose under a contract.
There is a silver lining, according to Mr McAdam. The cost of retrieving an item or payment may end up being more than the item itself is worth. Yet, he says it is always worth informing the trader.
So traders may reward an individual's honesty by letting them keep whatever item is sent in error - finally allowing the recipient to raise a glass to their good fortune.