There is a significant difference between taxis and transfers. The client may not know about it or consider it irrelevant. Your task is to explain why it is worth booking an individual transfer.
What you should tell the client:
When tourists take a taxi, all the risks of the trip fall on them: no one manages the trip, you have to keep track of the meter, bargain with the driver, exchange currency, look for a car for the required number of passengers and baggage. It is twice as difficult to do it all abroad, because of the language barrier, fatigue after the flight, and hurry.
With the transfer, almost all these concerns disappear. When booking a transfer, the tourist gets: