Why do real estate agents rather than homeowners handle 90 percent of home sales?

A good estate agent is worth more than his/her fees in negotiation/valuation skills.

A purchase of real estate is often the largest investment the average person makes. It is a legal transaction that requires professional skill in covering all the areas that need to be covered. The average homeowner has no legal training or background. They wouldn't recognize a legal problem in a real estate transaction. The sale and purchase of real estate requires experienced professionals from separate disciplines.

Realtors are often the first professionals one encounters when a decision has been made to purchase real estate. A realtor can help you sell your property and help you purchase property. They know the availability of units in various categories. They can help choose a property in an area within your price range. They are familiar with all the aspects of the communities they serve. They can offer invaluable advice and will negotiate for you. They have contacts with local lenders that may help with obtaining financing. They can help buyers and sellers zero in on their particular needs and of course, they have all the contracts that the parties must sign.
The parties should always be represented by an attorney in the actual sale/purchase of the property. Realtors are not lawyers. A transfer of real property is a legal transaction that should be supervised by an attorney who specializes in real estate law in your jurisdiction who will arrange to have the title examined, all municipal charges paid before you take title, and make certain all the documents are in order.