of thinking that The Trading Standards Institute is a government body.
It's actually a Limited company, originally set up in 1881 as a professional association, to represent the interests of its members. In its own words, the Institute exists "...to support, assist, inform and educate those who work in the Trading Standards Service or are professionally involved in Trading Standards legislation and enforcement....". It's not primarily an organisation that exists to help consumers directly, although it does a lot of very good work in that area.
The Trading Standards Institute does work very closely with the DTI on consumer issues, and is also actively supported in a financial sense, so it's hardly surprising that many consumers see The TSI as just another government department. It's not, however, and has to take care of its own finances - hence the sponsorship.
The fact that the Institute is inviting sponsorship for leaflet production is not at all surprising - many commercial organisations do the same thing.