Getting a good, relevant link from a trustworthy source can become a resource for you to drive a lot of traffic to your site while also making Google's algorithm recognize you as a reliable site but using bad black had blacklinks will get you in trouble.
Google considers the exchange of free products (or discounts) for links to be a link scheme regardless of whether you are giving or taking. Make sure that this link is a no-follow link, which is a link that has the rel="no follow" attribute to ensure this does not qualify as a link scheme.
Due to the fact that a website's footer appears on each page, this is a prime location for a link to be placed. It's likely that Google will be able to identify and penalize you for using commercial anchor text in footer links at scale to influence results if you've been adding them at scale to manipulate results.
If you try to game the system in such a way that you try to make a link appear in the exact same color as the background of your website, it will become apparent to Google that you are trying to cheat the system, and Google is going to penalize you for it. You might also consider the possibility that if you include plenty of irrelevant links, that will make it harder for Google to direct visitors to your target audience because your relevance would be diluted.
Website links may be able to be shared as comments, but make sure it is relevant to the website you are commenting on. The use of comments to build links is not really effective at all, and as such, you risk being penalized for being a spammer.
You might think it makes sense to make sure that the title of each link you share from your page matches what the page is about, since that is how that page works, and being consistent might suggest that the page is relevant. It is also possible from Google's point of view that this is an example of lazy spamming on the internet at random.
Websites that link to each other are called PBNs. During the 1990s and early 2000s, these types of pages used to be much more common, particularly among fan pages for various TV shows, movies, musicians, and other relevant content types.