While the "partner" approach -- in which advisors team up with other members of their clients' professional network to provide more effective and comprehensive solutions -- has won a lot of support in the advisory community, some of the details of finding new players to fill the holes remain a little vague.
For example, advisors are often called upon to refer clients to trust companies, insurance agents, specialized lawyers, accountants, and other professionals required to fill out all the necessary areas of expertise that a wealthy family may need on its team in order to meet its financial goals.
While the criteria for finding the right person are always going to be situational, there are a few constants. As a recent discussion of how to find accountants for your clients indicates, picking a potential competitor is obviously not going to work out well, so be careful before inviting a CPA who also provides investment advice into your clients' confidence.
Make sure they're team players. And get a sense of their fee structures in advance. Beyond that, it's probably a matter of finding a personal fit with your existing partners and, of course, your clients themselves.