Disclosure: I’m not a legal expert, and these requirements and guidelines change all the time. This is simply meant as a reminder and to link to the relevant laws / guidelines where they can be found.
It all depends where in the world you are located, which requires where a disclosure goes. This doesn't just apply to blog posts, this applies to anything which would require a disclosure (like sponsoring of a video, reporting of a company that is owned by the company that is doing the reporting, etc).
If you live in, or your company is based in the US, then the FTC requires that the disclosure be placed "where it easily catches consumers’ attention and is difficult to miss" and that a consumer may miss the disclosure if it's at the bottom. It's your exact choice where the disclosure goes, but the FTC makes it clear that it can't be difficult to miss.
If you live in, or your company is based in Canada, then Ad Standards are what you have to follow (it is a non-profit self-regulatory body). Disclosure should be clear, it should catch the viewers' attention and be placed where they are not likely to miss it. Disclosures should be specific about the brand, product and what was given. Disclosures should be clearly communicated.
In the European Union clicking on a link that ties back to the person who put in the link and that may collect someone's personal data, (under GDPR) you will have to disclose any such links that the links will collect someone's data.
In the UK, the ASA (Advertising Standards Authority) set the guidelines. If it's an ad of any sort you need to disclose that it is an ad.
China doesn't have the strict set laws that most countries do, however according to Freshfield Bruckhaus Deringer there is a patchwork of laws and regulations for online activity that have been used to enforce various disclosures and various other requirements.
India does have an advertising standards council ( The Advertising Standards Council Of India), however it is self-regulatory and a voluntary organization. Their principles are, honest representations, non-offensive to public, against harmful products and fair in competition.
Where should you put the disclosure? I think if you want to be honest, transparent, and show that you are following the law then put it at the top, or just after the first paragraph or two. The disclosure may be at the bottom when the editorial guidelines say so, or you don't feel the disclosure is completely relevant but you are putting it there just in case.
Thanks to VAMI Creations for links to some of the resources that are linked here.
In January 2021 I’m trying an experiment, I’m going to be posting at least 2 blog posts per week. This is not only to see how the engagement is, but how my writing goes over during the time. As always you can contact me directly if you have any thoughts or opinions on this or what I’ve written on. This is post number 58 as part of 100 Days To Offload.