An estimated 10 million small-business owners plan to sell or close their business over the next 10 years to fund their retirements, but many might be inadequately prepared to do so. That’s the key finding of a survey that revealed that less than 30% of owners have written business succession plans.

Recently released, the nationwide FPA/CNBC Business Owner Succession Planning Survey was based on responses from advisors that specialize in small-business financial planning and are members of the Financial Planning Association. The survey showed that 94% of advisors have discussed the importance of developing a succession plan with clients, but less than three out of 10 clients have proceeded with developing such a plan. That’s alarming, the poll revealed, because business owners are generally relying on the funds they hope to get from selling their business to fund 60% to 100% of their retirement needs.

"There is a huge perception gap among business owners of what it really takes to have a successful payday at the end of their career," Dave Yeske, CFP and managing director of Yeske Buie, told CNBC. "Selling a small business is not easy; it is very difficult to monetize a closely-held business."

Indeed, demonstrating the value of a business to potential buyers is among the top challenges would-be sellers face. Other challenges include letting go of a business emotionally (33%) and finding a buyer (28%).  

When owners do find a buyer, it’s often someone they know: More than half sell their businesses to employees (23%) or family members (31%). While selling to family members is prevalent, less than half of owners include family in the succession-planning process. That lack of inclusion occurs as owners face a myriad of issues when looking to sell to family. Challenges include equalizing the business owner’s estate with non-employee children (50%), distributing executive control among family members and children successors (45%), and uncertainty about family’s ability to run the business (42%).

When it comes to selling a business, most transactions are financed by installment sales (42%) or earn-out arrangements (34%). To help such sales go successfully, business owners can start developing a succession plan sooner than later. Ron Tamayo, CFP and principal of Moisand Fitzgerald Tamayo, told CNBC that a good place to start is to value a company’s business assets, and to then formalize and record business processes. This helps determine what actions encourage customer loyalty, sales and profits.