Even if they’ve been professionally cleaned, used school swimsuits are too dirty for this marketplace. Mercari is Japan’s largest online flea market, a place where individual sellers offer an extremely wide range of new and used items. It’s not just collectibles that Mercari deals in, either. Previously, for example, we’ve looked at the Mercari market for such niche products as ATM envelopes and curses. That doesn’t mean that Mercari will allow …