The ASA (Advertising Standards Authority) scrutinise every TV ad script prior to production and will demand corroboration or changes to be made when claims are made. I've had a few 'discussions' with them in my time.
Usually with technical or performance claims they will accept a report from an appropriate independent third party. So companies hire Labs to run tests etc In some circumstances and conditions, they must have got someone to achieve the results claimed.
The ads that amuse me are the cosmetic ads where close scrutiny shows unconvincing test results (68% of women who noticed a difference agree) from statistically dubious sample sizes (120 women surveyed)