Maddison Blue is a chain of high-end clothing stores in Adelaide, with locations in Norwood, Unley, and the CBD. The chain is owned by Maddy Highgate, a former lawyer in her mid-40s who has single-handedly developed the business into the successful enterprise it is today.

Maddy oversees management of all three stores, with a small team of retail staff situated at each of the stores. Each team consists of an assistant manager and two or three sales assistants. Each member of the team receives a salary (or hourly rate for casual staff), and also a commission bonus. For each sale made, the team member receives 3% of the sale price. Each member's commission bonus is calculated at the end of each quarterly (three month) period, and all employees are invited out to drinks with Maddy to celebrate. These quarterly drinks have become lively outings, with a friendly atmosphere of competition and accolades for the person who has achieved the largest bonus in the quarter, who must also buy the first round of drinks.

For the past two quarters the top sales earner has been Suri Charles, the assistant manager of the Norwood store. Suri is in her late 30s with over 15 years of retail experience. She was head-hunted by Maddy last year from a rival store. She enjoys taking a 'mother hen' role with her younger staff members and enjoys the social aspect of the quarterly drinks, at which she is known for her crude humour and being the 'life of the party'.

For the third quarter in a row, Suri is again the top seller, having made $42,560 worth of sales for the Norwood store. This is the highest amount ever sold by a Maddison Blue employee in a quarter. Her commission bonus is $1,277. Drinks are held later that night at Aloft Rooftop Bar in the Adelaide CBD. The other employees engage in some good-natured ribbing of Suri who must buy the first drinks. Everyone orders cocktails. Suri is feeling great about her bonus, and she buys everyone two cocktails each. Maddy attends the drinks, as usual. Maddy is feeling quite jovial herself, as it's been a very good sales quarter for Maddison Blue and Maddy is feeling very pleased with herself for having recruited her top-earner Suri last year. Maddy buys two bottles of expensive sparkling wine for the group. It's turning out to be a great night, with lots of laughing and loud talking.

Maddy leaves the bar to make a phone call and one of the sales team asks Suri about her winning sales in the previous two quarters. The group are tickled to learn that Suri's previous two totals as top-seller were $35,780 and $39,340, so she's increased her own total with each quarter. One of Suri's team members, Courtney, suggests that Suri should ask Maddy for a $5,000 extra bonus, in addition to her 3% commission, if she makes $45,000 sales in the next quarter. Everyone at the table agrees that this is an excellent idea.

When Maddy returns inside, the sales teams are loudly daring Suri to ask Maddy.'What the bloody hell is going on?' says Maddy. 'We were just saying,' said Courtney, 'that if Suri makes $45,000 next quarter, you should give her an extra $5,000!' Maddy takes a long sip of her drink, then looks at Suri and says, 'Make it $50,000, and you've got a deal'. Everyone explodes into laughter and claps loudly. Courtney writes '$5,000 for $50,000 sales!' on a napkin and takes a photograph of Suri and Maddy holding up the napkin and doing a 'Blue Steel' pose, which is an in-joke for the business. The group continue to drink and end up at a nightclub in the early hours.

Feeling worse for wear after her big night, Suri feels better when Courtney SMSs her the photograph the following morning with the text, 'Next time all the drinks on you!' Suri decides to devote the next quarter to selling as much merchandise as she can. She covers shifts for her team members at every opportunity and reads books and listens to podcasts on aggressive selling techniques in her spare time. Although Maddy usually drops in to the Norwood store weekly, Suri doesn't see Maddy for weeks because Maddy is busy setting up a new store at Marion.

Two months later when the monthly sales figures come in, Suri has made $32,000 worth of sales in the preceding two months. Suri sends Maddy a text message that reads, 'Better get ready with that chequebook, I'm headed for that $50,000!' along with the money bag emoji. Maddy replies with the thumbs up and smiley face emojis.

In the third month Suri steps up her aggressive selling techniques and comes in early every morning to ensure that stock is set up in a way that will maximise sales. Her team members are frustrated with Suri's tendency to jump on every customer who comes in the store, but they humour her as they know it'll all be over at the end of the month.

Finally, the quarterly figures come in and Suri is yet again the top seller, having sold $51,035 of merchandise for the store. Drinks are held that night as usual, but Maddy doesn't make it, still being busy with the Marion store. Suri emails Maddy the next day. 'Hi Maddy, we missed you at drinks last night. Was super thrilled to be your top seller again, and to make our $50,000 goal! Are you happy to transfer the $5,000 into my bank account along with my usual 3% commission bonus?' Suri receives a reply later that day. 'Hi Suri, congratulations on your amazing sales figures. So proud of you! You deserve every cent of that commission bonus. I've transferred all commission bonuses today. Not sure what $5,000 you're talking about? Your commission bonus is $1,532 this quarter.' Suri immediately writes back to remind Maddy about their agreement three months earlier, and remind her that she texted her a month ago. She even attaches the photo of the two of them pointing to the napkin. Maddy doesn't reply to any of Suri's repeated emails or phone calls. Maddy unfriends Suri on Facebook. Eventually Suri seeks legal advice and sends Maddy a letter stating that Maddy owes Suri $5,000, being the extra bonus commission the two agreed at the bar three months earlier. Suri threatens to sue for breach of contract if the money is not paid within 7 days. Maddy replies to say there was never a binding contract and the discussion that took place in the bar was not serious. She had no idea that Suri took it seriously but there's nothing she can do about that. She would never agree to giving $5,000 to an employee just for doing their job.

Question: Is there a valid contract?

A valid contract requires: agreement (generally offer and acceptance), certainty and completeness, intention to enter into legal relations and consideration.