From time to time I am asked to fix mistakes on projects that other companies did. Sometimes it can be tedious and I wonder how they messed it up, but then I realize that they were part of an incomplete team on a project. That is why we are different.
Some of the things I have seen (yes some from local professional companies!):
Web sites that load way too slow because of improperly sized images or 50 plugins installed in a WordPress site.
Insecure, hacked websites from a company that uses one outdated CMS platform for all their clients
Website designers that do not have the ability to support and fix their own platform they use, or know how to manage hosting or SSL certificates on a website.