If you transfer a Domain / Website, you typically get a receipt. That is what I experienced with DynaDot, even yesterday.
Also, I'm considering cleaning up my portfolio: eBay would be an excellent way to go; at least, I will try with an Auction.
And if it's that complicated and PayPal doesn't believe you, besides showing them the successful transfer confirmation, you can still check in WHOIS and contact the registrar.
Best
z