Scars in general and stretch marks in particular are problems that don't have easy solutions. People who suffer from these conditions are open to products that can promise to help them, but sadly there isn't a great deal that can be done about them. So a television advert highlighting a skin oil that women say has improved their appearance is quite likely to have an impact.
When Palmers ran an advert for their skin oil it had one impact that they probably would have preferred not to have. Somebody complained to the ASA that the claim couldn't be substantiated. I sympathise with the complainant. Applying an oil to a scar might increase healing time a little, but it is far from a panacea. But when the ASA investigated the claim the company were able to produce a report from a testing house which included testimonials from users.
The script the actors in the advert used followed the constraints of the test and the advert put up text with the specific statistics. In fact the results of the test were surprisingly good with 89 out of 100 women reporting that they felt the product had led to an improvement. So even with a tough to treat condition you can honestly make a very appealing claim for a product, just so long as you have the data to back it up and resist the temptation to over egg the custard.