What happens if my child can't actually afford to buy the business at a fair price?

There's no requirement that a child pay full fair value up front. Parents commonly address this with vendor take-back financing — payments over time rather than a lump sum — a mix of gift and sale, or more flexible price and payment terms than a bank or arm's-length buyer would accept. What matters is documenting whichever approach you choose clearly: if part of the value is effectively being gifted through generous terms, that should be understood and recorded as such, rather than left ambiguous.

Whatever structure you settle on, an independent valuation is still worth getting, so everyone has a clear, defensible sense of what the business was actually worth at the time, even if the final terms end up more generous than a stranger would receive. If your child genuinely can't afford any meaningful purchase, it's worth being honest about whether this is really a sale or effectively a succession gift, since that distinction affects both the tax treatment and how the transaction should be documented.