Paying a an upfront commission makes no sense however it is dressed up: companies trumpet that declaring their upfront commission means that their pricing is 'transparent'. What matters is the price the investor pays for the wine – full stop. An upfront commission makes no sense because generally buying the wine, with certain rare exceptions like Pétrus and Le Pin, is the easy bit. It is much harder to sell wine, especially at a good price. Usually companies charging an upfront commission will not levy a commission on sales. Fine but what incentive do they have to sell your wine?
What happens if the company has ceased trading when you want to sell your wine? You will be faced with paying a seller's commission to another company. This means paying twice over (both when you bought and when you sold) and it is worth remembering that wine tends to be a medium to long-term investment.