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's trying to hedge his bets on the shipping to make sure that it's not heavier than he thought after it's packed up. OTOH, if you are paying a %, it shouldn't matter how many invoices it's broken into.
I'm with Swampwalker on this. He's probably been burned
in the past by under-calculating shipping. You're not
paying the fee twice because 3% of the total will always
be 3%.

If you pay $1000 + 3% it is $1030. Then shipping costs
$50 + 3% = $51.50. Or if you paid the full amount plus
shipping it'd be $1050 + 3% = $1081.50. $1030 + $51.50 =
$1081.50. Break it up or combine it. Percentages don't
change.

But it definitely is an odd way to go about selling an
item nonetheless.
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.