There are so many nuances to each individual's tax situation that it's impossible to give advice based on the existing question/information. The seller should consult with a CPA, tax attorney, or other qualified professional.

Seller, especially anticipating high gains, needs looking into a trust owning a note structure where all gains/profit, if kept within trust no payouts/dividends [expenses excluded{hint}] - are tax exempt. Yes, there are trusts of such type where trust buys property, has expenditures etc. and you know who benefits, yet only payouts are taxable, which, if properly done, never happens, and beneficiaries may take non-taxable loans etc. Very viable route and no, chatGPT will not help you.