yep, usually a quick message clears things up, especially when you're waiting on an invoice, it's an easy thing for a seller to forget, especially now when you can check ebay on your phone, where you can't do such things as invoices.
Sometimes I'll see the message, but I'll be out and have to get home to a PC before I can adjust something - I'll usually message the buyer that, but sometimes messages just don't send, you lose service, or the app or your phone does something wierd, and they just don't get the message. It's always best to give them at least 24 hours to respond before shooting off another message, unless of course you forgot some info, or they've contacted you back. I know I'm a shift worker, and I get grumpy when I get home from work and there's several messages from a buyer about something I can't do anything about until I've had at least some sleep and can stand a monitor in my face, lol!