What expert advice is worth buying? Please be fairly specific and include some conditions on when someone should consider getting such advice and focus on individuals and families versus, say, corporations.

I ask because I recently brainstormed ways that I could be spending my money to make my life better and this was one thing that I came up with and realized I essentially never bought except for visiting my doctor and dentist. Yet there are tons of other experts out there willing to give me advice for a fee: financial advisers, personal trainers, nutritionists, lawyers, auto-mechanics, home inspectors, and many more.