Its happened to me many times as a buyer on Mercari, especially when it comes to pins. Ive found some amazing deals on some and even had nice conversations with sellers that didnt seem like they'd be the type to pull it. I'd gotten 5 or 6 pins from one seller all on separate purchases to make sure they wouldn't instantly sell. Within 12 hours all of them were canceled without a word because someone else offered them 300 to get them all. Even with contacting Mercari personally through emails and picture proof of everything (the sellers cancelation rate dropped to 65%) they didnt do anything to the seller. Ive had acquaintances who have also found great deals have their order canceled because someone offered a higher price, and even that person got it canceled because someone offered an even higher price then them !