I usually buy them from local bookstore in bulk (after a number volume of series is released).
They served as a collection purpose in my bookshelf. Only read it when I feel nostalgic.
In my opinion, buying from store links is not an option, since not all language is provided.
I do respect the purpose of supporting authors, but the problem in most people case is, not every manga is translated in their respective language. And since they are not a Japan residence, the only way to find new interesting series (that will worth the time to read) is from manga website. This is actually an indirect marketing for the author.
Recently, Shonen Jump has actually see that positive side. They decided to make the big move and provide a new chapter of series for free. Of course you cant read the whole volume series, but how they put the pieces is already served the content purpose, as a teaser. People read, found it as interesting, then they will surely buy.
But again, I do wish that all manga could be licensed around the world, so the purpose of supporting authors could actually be true.