First time seller

I am new to selling on CardMarket so I am not sure what to do here or if this is sketchy on that persons behalf, any advice will do.

Long story short, the shipping is 100 as the cost of the card is over 300. The guy wants a refund once he’s confirmed arrival of 60. Which to me is fine since shipping only costs around 30 for insured and tracked. But is there any reason card market has it so high? Is there something I don’t know or understand? Before I say yes to accepting the refund agreement I’d just like to make sure this guy isn’t trying to scam me or something.

Thanks in advance !