By scanninq QR codes you were directed to Austrian post website, as these stamps were officialy created by them.
Crypto.post.at you can verify stamps by their ID.
Austrian post have issued 150,000 stamps total.
Rarity of these two stamps are
1/10 (0.007% of supply)
And 1/53 (0.035% of supply)
Both are gems, onchain stamps with rarest property: "sold"
My blue stamp with 5 digit lenght ID is the rarest blue stamp  (10 only made) another with 6 digits is 1 from 53 on earth.
Both stamps are very rare, they are worth easy twice more as im asking.
I will repay the loan and take them back, i am collector myself.
I will probably repay more faster than 1 week. It could be a day or two, but to be sure all is perfect lets set a term for a week and ill be on time

ERC721 tokens , can be sent to escrow/lender ETH wallet