An essay-writing company has had its adverts banned after they were deemed to be misleading to students.
The Advertising Standards Authority ruled that UK Essays had failed to make it clear that the papers were not meant to be submitted as students' own work.
The online ad also gave a "misleading impression" that the firm had received positive press coverage, the ASA said.
UK Essays said it would ensure its fair usage policy was more prominent within the website.
A website for ukessays.com featured text that stated "guaranteed grade, every time. We're so confident you'll love the work we produce, we guarantee the final grade of the work.
"Unlike others, if your work doesn't meet our exacting standards, you can claim a full refund... loved by customers & the global press UK Essays have lots of press coverage from all over the world confirming that a 2:1 piece of work produced by us met this standard... We were the first company in the world to offer you guaranteed 2:1 and 1st class work".
Extra information about the service was included on pages entitled World Class Guarantees and UK Essays in the Press, the ASA ruling explained.
A complaint was brought by the Quality Assurance Agency for Higher Education (QAA), a universities watchdog, which argued that the ad was misleading because it did not make clear the risks associated with submitting bought essays.
It also said that references to the press coverage UK Essays received implied that they had had positive coverage or endorsement from these media outlets.
Upholding the complaint, the ASA said: "We considered the ad gave an overall impression that consumers would be able to submit the purchased essays as their own, particularly because of the anti-plagiarism and grade guarantees.
"We considered that consumers would understand from the website that they could purchase an essay of a particular grade that was plagiarism-free, and that they would be able to make a claim under the refund guarantee if they submitted the essay and did not receive the grade ordered, or if the essay was found to be plagiarised."
It added: "Because we considered consumers would expect from the ad that they could submit purchased essays as their own that would meet the ordered grade without risks, which was not the case, we concluded that the ad was misleading."
In February last year, the then Universities Minister Jo Johnson urged university and student bodies to do more to deal with the spread of what he called "essay mills".
'Respect the decision'
A spokesman for UK Essays said: "While we are disappointed with the ASA ruling, we respect the decision and we look to ensure that our fair usage policy is more prominent within the site.
"We pride ourselves on the quality of work we produce, but ultimately, we are happy to work within the provided guidelines.
"We are committed to working closely with any educational institution who are happy to work with us and create open working relations going forward.
"Our desire is to become the word's leading educational support service and we firmly believe that working closely with universities and educational bodies all over the world we can achieve this."
Welcoming the ASA's ruling, QAA's director of academic standards Ian Kimber, said: "Essay mills mislead students and put their academic and professional careers at risk.
"This landmark ruling by the ASA is the first successful challenge to their claims of legitimacy, exposing their cynical use of anti-plagiarism disclaimers and exploitative media referencing.
"We will continue to campaign for academic integrity, supporting both students and higher education providers in identifying and tackling cheating and other abuses.
"This case helps to spread the message that cheating, in any form, is unacceptable."