I can start up Steam in offline mode and play games. I can do this with my Internet connected fully, partially, and with my router switched off. I can do this even if the router is switched on when I close Steam, and switched off when I start Steam. Do I get errors? Occasionally, yeah. But this is a persistent bug where you have to start Steam twice.
It kind of doesn't surprise me really that most people wouldn't think of trying again after receiving an error, but I do, and it always works. Every damn time. I've mentioned this in the past, too. Because there was one point where restarting Steam twice was actually necessary to get into offline mode, whereas these days it's just a rather rare bug. But really, just close Steam completely, then restart it and try to get into offline mode. Does it bug out on you, then? It probably won't. Deleting files is not necessary.
I haven't had a problem getting into offline mode since Steam's launch, and I haven't magically started having issues today, either. I've spent months in offline mode for various reasons, and it's never failed me.
So I'm just baffled as to what everyone else is doing wrong.
Unless it's really true that no one knows about the double-restart thing.