I know this answer is a little late, but I figured I would answer anyway, in case someone else has a simalir question/issue. In regards to Mercari you are covered as a buyer as long as you pay through the Mercari app. Any off app transactions are prohibited and there shouldn't be any reason a seller is trying to get you to pay outside of the app, unless it is a scam. Now if you were to purchase said iPhone through the Mercari app you are covered as a buyer because Mercari holds the funds until you as the buyer recieves the product and then rate the buyer before funds will be released to the seller. If you either do not receive the item or item is not as described or damaged, you will be refunded your money. Also now all that being said if you make any purchase with PayPal make sure it is not with the friends and family option because you will not be covered with PayPal's buyer protection.
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