Another theoretical option is to allow the client to sell the financier's units to third parties at market prices, while the financier may also quote a price at which he is willing to buy. This can introduce new partners and disrupt the planned exit, so periodic valuation and client purchase is usually the more practical route.
The essential idea is gradual transfer of real ownership. Every payment should therefore be understood according to its true function—rent, profit share or purchase price—rather than treating all payments as one undifferentiated installment.