Whichever way you look at it, you need to find someone you can feel comfortable with and be honest with. Over time as you build a relationship with your mastering engineer they will understand more and more your taste and what results you are after.
It’s taken a few years for me as a producer to find someone who clicked for me as a mastering engineer but happily I stumbled across Panorama Mastering and thankfully, haven’t looked back.
At the end of the day, as mentioned above by Nicholas, it’s all about the music. No mix or master will savour a poor written/recorded song! But create a killer song and an excellent mix and master will give it the best fighting chance in an over-crowded pool of music to shine!
Best of luck!
Spike Leo