As programmer we often get involved in discussions about the best way to implement a feature on a site. We can talk at length on why LESS is better than SASS, or why WordPress is a great base for an application framework and Ruby on Rails is a bad idea. Some other programmer can also reverse any of those arguements, and everyone could still be right.
The reality is that clients want solutions to problems. They don’t care about LESS or SASS. They don’t care if you use WordPress or Rails, they just want it to solve their problems.
To that end, sell yourself as a problem solver. Don’t push your Rails on them if they just want a blog redesign and already have WordPress. Help them find a WordPress developer that can build a new site for them.