If the website is approaching you selling backinks, talking about how great their DA is, or are selling links from Amazon, chances are its a scam. What a lot of these people do is buy expired domains that already accumulated DA then populate them with spun content.

Always ignore these fools.

If you want to buy real link, Google your main keywords, find sites already doing well in your niche (thus already making money without selling links) and ask them for links or a blog post.

Its also better meeting people in your industry rather than these link selling idiots because you network with useful people.