Really good question.
I have I asked this question to myself a lot of times when I actually buy things or when I'm looking for a service I could use.
From my experience I can definitely say that I never bought something because it looked good. But when I had two alternatives and one looked better than the other I catched myself tending to the better looking service which was not always the best service provider. A company which has what I need and has also a great design / UX gets a big plus point.
But what I also learned is that a good structured site with intuitive navigation is really good makes really solid impression. By intuitive I mean guessing where you could find informations you are looking for. For example documentation of the API they are providing.
From my experience I can definitely say that I never bought something because it looked good. But when I had two alternatives and one looked better than the other I catched myself tending to the better looking service which was not always the best service provider. A company which has what I need and has also a great design / UX gets a big plus point.
But what I also learned is that a good structured site with intuitive navigation is really good makes really solid impression. By intuitive I mean guessing where you could find informations you are looking for. For example documentation of the API they are providing.