common housing practice Goshiwon

Hello,

My son is going to university in Seoul for a semester and we are looking for accommodation. I contacted a landlord in Goshiwon who asked us to pay $300 on paypal and to pay the 1st and last rent in cash on the day of arrival. Then to fix a date for the payment of the other rents in cash. He also said that if we didn't respect the rental period fixed at the start, he would keep the $300.

Is this a common practice in Seoul?

Thank you very much.