Even with new shoes, sizes can vary
dramatically from one brand to another, and even in different styles of the same brand. I typically wear an 8 1/2, but I have size 8s and 9s and even one 9 1/2 in my closet because of the way they vary. And that's with NEW shoes. With vintage items, all bets are off.
Buying shoes online is a supremely bad idea if you are not prepared to ask some very detailed questions and will be unhappy if they don't fit. Shoes are simply one of those things you must try on first before you know whether they'll fit, no matter what the tag inside says.
BTW, I used to sell shoes, so I know what I'm talking about.
Must use Buy It Now and PayPal.
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You have two choice, assuming you used PayPal or a credit card to pay. You can decide to keep the one pair that fits and eat the cost of the other, or start a PayPal claim or a credit card chargeback for an item not as described. When instructed to return both pair to the seller at your expense with tracking and PayPal will refund your original payment. 
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