I do not buy all my Apps from the Mac App Store, but I buy many of them there. It is just easy to do and a very secure process. One problem with Apps on the Mac is whether or not they are supported by the Developer. If you look closely, you will see that some Apps have not been supported by the Developer for several years. Those are Apps to avoid, they will not work with current versions of macOS or at least will be obsolete very soon. If you are buying an App from the Mac App Store, you can determine if it is currently supported by checking the Version History. Here is how you do that.
First, select an App in the Mac App Store. In my case, I have selected Affinity Photo.
Somewhere on the App information page you will find the “Version History” link. Just click on that to go to this next screen.
In this case, Affinity Photo was updated 1 week ago and 1 month ago before that. It is clear that this App is being currently supported by the Developer. If you see an App that has not had a new version if a couple of years, you know the Developer is no longer supporting that App. Or, maybe you could contact them to make sure one way or the other. If the App is no longer supported, it is better to find another App to perform the same function that is being supported currently.
One problem with buying Apps is some of them are old and no longer supported by the Developer. This problem can be overcome with a little research in the Mac App Store.