Before listing a home, sellers usually see two kinds of value estimates: a comparative market analysis (CMA) from their agent, and, less often, a formal pre-listing appraisal. They can look similar on paper. They're not the same thing.
A CMA is an informed opinion
An agent pulls recent comparable listings and sales, adjusts for differences, and lands on a suggested price range. It's useful, and most agents are good at it — but it's not performed under any licensing standard, and it can be influenced, even unintentionally, by an agent's incentive to win the listing.
An appraisal is an independent, licensed opinion
A pre-listing appraisal is performed by a state-licensed appraiser under USPAP, the same standard a lender's appraiser will apply later in the transaction. That means the number is independently verifiable and carries more weight if a buyer's lender appraisal ever comes in for a debate.
When the difference actually matters
For a typical, straightforward home in a well-documented neighborhood, a good CMA is often close enough. The gap matters more for unusual properties, thin comparable sales data, high-value homes, or when a seller wants a second, unbiased opinion before committing to a number.
The two aren't competitors. Many sellers use both — the agent's CMA for market positioning, and an independent appraisal as a check against it.