What I would say about influencers is that some of them have pull and others don't, just like any other marketing strategy. What an influencer might be able to do for one product is not a guarantee they'll be able to duplicate it every time for others. There are too many variables, and followers of influencers aren't all automatons. Even if they do like the influencer, or other products they've showcased/backed, doesn't mean they will like them all.
So, it's going to depend on the influencer, their base, the kinds of products, the background, reason for being influential, and expertise of the influencer, the enthusiasm of the endorsement, what the companies working with the influencer do with the buzz they do get, etc.
That said, people do like having someone they trust recommend products and services. That's why word of mouth, even in this day and age of the Internet, is still king when it comes to marketing. Reviews and influencers tend to be the digital version of this, but I think we're still more likely to try something a friend or family member suggests before we're going to trust folks we don't know.
I don't tail any because I don't know any influencers in real life. I've been on both side of the marketing fence, and so I have some understanding of how things work, and mostly don't work. If the influencer has some expertise in what they're trying to endorse, that's a little better than if they're an Instagram celebrity hyping something that has nothing to do with why they're a celebrity.
In any marketing endeavor, targeting and drilling down to folks who are actually interested in any given item or product is becoming the norm, rather than any sort of shotgun approach. There could be a myriad of reasons why an influencer is followed, and a lot of it will have little to do with the endorsements. If there's a million people following an influencer, it's likely only 10,000-20,000 (1-2%) of those folks will be interested in any given item at any given time, and that will be spread over many different items.
In other words, an influencer's audience can be fractured into smaller groups just like any other.
So, the key to using an influencer becomes only trying to market what that influencer is specifically known and trusted for. Don't have a fitness model trying to sell diapers. Might work, but more likely, it won't, unless somehow she is also a trusted source for diapers.