That's part of my evaluation process when I need non-technical services like plumbing. If the website contains the relevant information but is an eyesore, I feel that they prioritize doing good work over fancy marketing materials.

Good work shouldn't only be done in your focus/product area. If your accounting, project management, or, yes, marketing sucks, you'll fail.

For many things, yes. Local plumbers will often get most of their work via word-of-mouth, for which doing good work is necessary. In which case, being terrible at marketing to me signals that your work is good enough to stay busy without trying.

Note, there is absolutely nothing scientific about this claim of mine. Just a made up heuristic that seems plausible to me.