You need all three, and they do different jobs. The advisor runs the process and the negotiation, the attorney drafts and negotiates the documents, and the CPA models the after-tax outcome before the structure is set.
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The most expensive mistake owners make is using their long-time general-practice attorney for a transaction they have never done. Purchase agreements carry representations, indemnities, escrow mechanics, and survival periods that are their own specialty, and an attorney who negotiates them regularly will save more than the fee difference in one section. The CPA's work has to happen earlier than people expect: the difference between an asset sale and a stock sale, or between allocations across asset classes, can swing the after-tax proceeds by a large margin, and that analysis has to inform the negotiation rather than follow it. Most transaction attorneys and transaction-experienced CPAs in this region concentrate in Charlotte.