It has also cited a number of sectors, including pay-day loans companies, cosmetic and healthcare providers, and "freemium" video games and apps, as set to come under increasing scrutiny.
In its annual report, the ASA reported it had received 31,298 complaints about 18,990 ads over the course of the past year, with 3,700 ads charged or withdrawn.
This marked a small fall in the number of overall complaints, down from 31,458 in 2011, although the number of ads drawing complaints fell by several thousand from the total of 22,397 in the previous year.
In its extended remit covering online advertising, the ASA dealt with 6,273 complaints of 5,338 online ads, representing 28% of its total workload.
The majority of cases fell into the category of being "misleading", rather than harmful or offensive, and Committee of Advertising Practice (CAP) chairman James Best told Marketing this is where its focus lies.
"The vast majority of complaints are where people think they’ve been ripped off somewhere," said Best. "That is what we care about most. Most offenders are way outside the mainstream but we still have a responsibility to sort them out.
As part of its annual report, the ASA has identified the following five areas as "priorities" for the coming year:
- Free trials, where customers were unwittingly tied into an on-going paid relationship after signing up for a free offer.
- Misleading pricing, such as forcing the telecoms sector to offer clearer information on price packages.
- Daily deals, combating "widespread problems" such as failing to conduct promotions fairly.
- Misleading testimonials, ensuring testimonials are genuine and improving transparency around paid endorsements by celebrities.
- Misleading health claims, playing a part in protecting consumers from misleading and potentially harmful ads.
The CAP revealed it had been required to deliver record levels of support to advertisers, providing advice and training on just over 100,000 occasions, including 6,779 requests to its Copy Advice service.
According to Best, smaller brands are increasingly seeking out advice to ensure they avoid misleading claims on their websites.
He said: "There is quite a big education job because, with a lot of complaints about the websites, they just don’t really know enough about how to behave well. That is where the copy advice services come in."
Best described himself as "genuinely quite surprised" at the levels of willingness shown by advertisers to comply with regulations around advertising on social networks such as Twitter.
He added that the marketing industry continued to "mend its ways" with proactive steps to comply with the finding of the Bailey Review, ensuring children do not come into contact with overly commercial or sexual advertising.