If it doesn't cost you any extra to buy from that link what are you losing by doing it?
Yes - they are selling you something, but that's why most of those people are on social media in the first place - to make money via increasing awareness of their brand, getting advertising fees from a 3rd party or actually selling stuff.
But you are not alone - there's tons of psychology research done on how people feel annoyed at someone gaining something even to the point of sacrificing our own gain to stop that happening:
From www.psychologytoday.com/us/blog/the-big-questions/201703/wanting-less-so-long-others-dont-get-more:
A whole host of experiments have asked people in groups of two to divide a small amount of money, like $10. A person is chosen at random to be the initial splitter of the money. They decide how much they want to offer the other person. The other person can then decide to take the money, or to reject the money. If they reject, neither person gets anything. In other words, if you get offered $2 knowing the other person is going to take $8, do you agree? This is a one-time decision, so your choice will not reflect any potential future earnings.
In one study, the initial person was actually in on the experiment, and was told to offer $8 for themselves and $2 for the actual participant, or to offer $6 for themselves, and $4 for the actual participant.
The results – I think – are super interesting. From a purely rational perspective, people should always take the money offered. It shouldn’t matter what the other person is getting or if it is an even split, because any amount of money is more than what you have. And from a rational view, people should maximize their own situation.
But that isn’t what happened. In the U.S. sample, 85 pecent of participants offered $2 rejected it (believing that the other person would get $8). This was the case whether the other person was a friend or a stranger. When the amount was $4, 58 percent of people rejected it they believed a friend was making the offer, and 30 percent rejected if they believed a stranger was making the offer (believing the other person would get $6).
That is, quite a high percentage of people were more willing to take no money than to let the other person take a higher amount of money than them.