Potential seller's strange policy


Is it normal when a potential seller requires that I make a PayPal payment for the item, then, when he receives the payment, he will pack the item, calculate the shipping cost and issue another invoice for shipment?

In such a case, I would have to pay a PayPal fee twice, and I am not sure what form of shipment he may choose, though I informed him of my preferred form of shipment.

I feel uncertain - usually, the shipping cost and the form of shipment are agreed upon in advance and paid once.

Any comments?
transl
He charged 4.25% as PayPal fee (not 3%) and tried to charge 7% as E-bay fee (but subsequently changed his mind).

In the meantime, I borrowed a similar item to figure out whether I like it or not, and then will decide.
this isn't strange at all. He probably wants to lock in the sale before going to the post office for a quote, then have the buyer back out.

Go to post office for quote? With potential buyers zip code and product weight, he can get all the quotes he needs online.