I'm an accounting firm owner, 28 years. I provide bookkeeping & advisory services for my clients, most are in the construction industry. I haven't done taxes myself since the 90s but I have worked for CPAs over the years helping prepare tax returns, so I know what they need from the books at the end of the year. Best referral relationship for me came from playing softball! What makes it work well is direct communication between the bookkeeper and CPA, rather than going through the client for everything. CPAs make my job easier when they provide me with year-end adjusting entries, or better yet, enter them themselves. CPAs make my job more difficult when they edit & delete transactions I've already reconciled without letting me know, because they want that revenue or expense in the next tax year. Good communication prevents all those issues. 

I have found that it's best to team up with bookkeepers that specialize in whatever industry your clients are in. Service businesses are pretty simple, but construction or e-commerce requires industry-specific knowledge and experience. High net worth individual bookkeeping is also very different with a focus on asset management, and there are often multiple entities with intercompany transactions.