David Beckham and Roy Keane, until recently team-mates at Manchester United, are world-class footballers. But as brand ambassadors, they are leagues apart.
Vodafone shifted more than 50,000 Live! mobile phones in the three weeks after England captain Beckham began endorsing the brand. But soft drinks brand 7-Up endured a far more unpleasant experience with its sponsorship of erstwhile Ireland captain Keane, when he stormed out of the team and was subsequently sacked after a disagreement with manager Mick McCarthy just days before last year's World Cup finals.
7-Up had signed a £500,000 nine-month deal with Keane that saw him appear in TV, billboard and radio ads. His face also featured on millions of cans, packaging and in-store promotional material. Keane's rancorous departure from the Far East left a brand marketing campaign in tatters.
While athlete endorsement can be highly effective, then, it is clearly not without a potential downside. "Of all the sponsorship alternatives, creating links with an individual carries the highest risk," says Hill & Knowlton group managing director for sports marketing and sponsorship Alun James. "There is the question of their behaviour or they could lose form or break a leg."
Recent stories focusing on the unpalatable - and in some cases, criminal - behaviour of certain Premier League football players has underlined the importance to marketers of not jeopardising their brand image by signing up sports stars whose actions might be damaging.
"The biggest thing for me is really getting involved with the athlete or team," says Ketchum Sports Network director Steve Martin. "You need a proper relationship. It's high risk - if something goes wrong, you have to be prepared. Work with the right agents and make sure you actually meet the athlete. Some people sign up without having sat down with the athlete."
So how do you decide who to use? The first step is to look at the sport and ask whether it fits with your brand. Some agencies have sophisticated matching tools, such as SportZ, which is used by a number of WPP-owned agencies.
Once you decide on the sport, draw up a shortlist of appropriate athletes based on their public profile, backgrounds and breadth of their appeal.
Look at the other products they endorse. Are any in competition with yours? Do the other endorsements have an image that may conflict with your positioning?
"Why does Royal Bank of Scotland use Jack Nicklaus and Visa, Sir Steve Redgrave?" asks IMG Consulting senior vice-president Graham Walpole. "Most tie-ups are where the company is associating itself with an individual of stature or authority. Where it is more dangerous is where the brand is rebellious, cool or anti-establishment."
Most contracts now include a termination clause that can be activated should the athlete do anything to bring either themselves or their sport into disrepute. There are also clauses designed to prevent damaging publicity if the celebrity is seen, even inadvertently, to be endorsing a rival product - as happened with pop singer Britney Spears who, while endorsing Pepsi, was allegedly spotted drinking Coke. Most contracts forbid the celebrity from endorsing, intentionally or not, a rival brand for several years after their work promoting a brand ends.
What makes a good endorsement? One widely held as being successful is Anna Kournikova's work for Berlei's Shock Absorber sports bra carrying the memorable slogan 'Only the ball should bounce'. Kournikova's form on the court has been poor of late, but she's been a smash with commercial deals. Shock Absorber sales had a 150% uplift in the wake of the campaign.
Sports stars can also be used to reposition a brand, as Lucozade has done by using a stream of athletes from Daley Thompson through to Michael Owen. "Lucozade used to be associated with old people in hospitals," says MEC Sponsorship director Ben Smith. "Its endorsement by sports stars has really turned around how it is seen."
MEC works with Visa and has signed up rowing colossus Sir Steve Redgrave as a mentor for up-and-coming British Olympic and Paralympic stars it is sponsoring in the run-up to next year's Games. "The idea is that a Visa card is empowering - it helps you to lead your life the way you want to," says Smith.
One of the UK's brightest Olympic hopes, long-distance runner Paula Radcliffe, has endorsements with Nike, Vittel and Cadbury. The latter link might have been tricky, says Walpole, as chocolate is hardly a health food.
But Radcliffe is a confirmed chocolate fan - Cadbury made great play of the fact that part of her payment would be in chocolate bars - and she fronts the company's 'Get Active' initiative for young people, making the brand fit a good one.
The effectiveness of some sponsorships are easier to quantify than others.
There is a clear correlation between Nike's huge sales increase in the golf market and the association of Tiger Woods with the brand, says Karen Earl Sponsorship account director Dominic Curran.
Assessing effectiveness with non-sports brands may be harder and depends on the aims. Paul Whitehead, UK account manager at sports communications research firm Sport+ Markt, says that if "image transfer" is the intention - if a brand is to be reinvigorated by association with an athlete - perceptions should be tracked.
He cites Beckham's involvement with Brylcreem, with the product seen as "an older man's brand" before its rejuvenation through its associations with the footballer. In most cases, metrics should be put in place to track sales impact and return on investment.
Brands tend to want to associate themselves with the best athletes, which has led to endorsement price inflation. As Octagon Athlete Representation vice-president Clifford Bloxham points out, when looking at the England rugby union team, "brands would rather pay more money for Jason Robinson or Jonny Wilkinson (than other team members) because research says they are known and exciting".
Sports star endorsements are not to be undertaken lightly. But the best can work wonders on a brand.
SIX OF BRITAIN'S BEST
Last month, the England captain said he was turning down new commercial offers to focus on football and parted company with long-term agency SFX. But he will continue to work with his current array of sponsors, which include Pepsi, Adidas, Vodafone and Marks & Spencer. In Japan he endorses Meiji confectionery, TBC health clubs and Tsubasa Systems 'car clinics'. Agent: Tony Stephens
SIR STEVE REDGRAVE
The five-time Olympic rower and one-time Walkers ad star is a 'mentor' of UK Team Visa, leading a team of six Olympic and Paralympic stars sponsored by Visa. He also endorses Johnson & Johnson's Lifescan blood glucose monitor and has his own range of leisurewear, branded Five Gold. Agent: Athole Still.
The tennis ace keeps his whites pristine with the help of Ariel and makes sure he doesn't dehydrate thanks to Robinsons. He has equipment deals with Slazenger and Adidas. Agent: IMG.
The dashing 23-year-old Formula 1 racer endorses Marks & Spencer's MW range of underwear and leisure clothing. He is also sponsored by Telford telecoms and technology company Glow Telecom and Japanese entertainment and music group Rosso, whose name appears on his crash helmet. Agent: Essentially Motorsport.
Rugby union superstar Wilkinson is another Adidas man, appearing together with Becks in its current TV ad campaign. He also endorses Lucozade Sport, Hackett clothing, The Times and has an ambassadorial role for Lloyds TSB. Other smaller deals include a link with Electronic Arts' Rugby computer game. Agent: SCG.
The record-smashing, long-distance running phenomenon is, like those other sporting giants Michael Jordan and Tiger Woods, a global ambassador for sportswear titan Nike. She endorses the Cadbury 'Get Active' programme and water brand Vittel - a sponsor of the London Marathon. She also has a licensing deal with Beurer, which sees her signature appear on-pack for products such as bathroom scales and pulse monitors. Agent: Octagon.