It depends where you are based but in a lot of countries, bloggers and social influencers are required by law to disclose a sponsored post. You can usually simply ask the influencer to add the mention #ad or #spon to their social post, or to add a small disclosure at the bottom of blog posts, to make it very clear and to stay out of trouble.
For the UK, please consult ASA to fully understand the online advertising rules.
For the US, please consult FTC to fully understand the requirements.
For AU, please consult ANNA to fully understand the advertising regulations.
Check out our blog post for more info on disclosure.