Well at a bare minimumbare minimum, adverts should not contain content that would be moderated if it was included in a question or answer. This includes:
- inappropriateInappropriate or NSFW imagery of the kind that would be put in a spoiler block if it was needed in a question or answer.
- Scams or misleading claims that would be illegal in print advertising in countries where this is regulated (there have been a lot of examples reported of fake-medicine "snake oil")
Many SE sites are professional and used in a work context. A bare-minimum rule of thumb should be, if an advert should neverallowed ads should never cause an office worker to think "I hope my boss doesn't see this trash on my screen". cause an office worker to think "I hope my boss doesn't see this trash on my screen".