In my area any car that doesn't need any reparation or work being done on it is sold at a minimum of 900€ and speaking of Clio of that era they are more like between 1700 and 2000€ if you want one in working order.
That is the funny thing with the second hand market. 20y old cars sold 20k€ or 80k€ new are sold more or less at the same price 20 years later. Because of higher maintenance cost and parts price + higher number of stuff that can fail, the more luxury items are also the ones that are less wanted and people looking for inexpensive cars will favor the most sold small cars of that era they or an independent garage can fix easily and cheaply.
Probably the fact that he's not Dutch, doesn't live in the Netherlands, and while yes you are 100% correct that the law is on his side and should be able to just return it for a full refund, it might be a task so daunting for someone who is from a different country that he just doesn't want to attempt it.\
EDIT: oh wait, he did do that actually:
>> On January 5, 2025 I called Tesla Netherlands Sales Department to request the return of the vehicle and a refund of my money.
Sounds like he should contact a dutch lawyer to send them an official letter informing that he's returning the goods as unfit to use.
I'm not sure why he's got problems returning, I'd expect Dutch consumer protection laws to make this an open and shut case.