I have always sent items before I got paid for them.
When payments were made automatically, my sales finished at the weekend, I posted on Monday snd then got paid on Tuesday.
You can use Simple Delivery. The buyer pays Ebay who send you a QR code to print and use or you could use a credit card to pay for postage and then pay the card off monthly with Ebay earnings.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)