"If they have developed a personal relationship with their advisor over many years or decades, investors may deem a split too awkward, especially if they run into their financial planner at social events (or if they happen to be relatives)."

The above quote should be a compelling reason for one to seek another advisor.  The fact that the social relationship has become more important than the financial relationship is a huge red flag.  Your ability to rationally and critically assess the advisor's performance is compromised by the element of worrying about their feelings or how they will react if you question their advice.  

The investor should never forget that the advisor (as good as they might be) still makes their living selling you a service.  Further, that advisor usually has an employer who expects them to out perform last year's targets.   Of the three individuals involved in the relationship guess who holds the weakest position?

Don't invest via friends or relatives.