Shouldn't it be 'everything was sold out' instead of 'everything is sold out'? I mean 'sold out' already means that something has been sold out. It has been sold out in the past.
Ah, I think I know what the difference is now. Thank you, Marius Hancu.
So, 'The books were sold out yesterday' has the same meaning as 'The books are sold out now'. Am I right? Also, I wonder if I could say 'The books are sold out today'.
Sorry but I still don't completely get it. I mean in your sentence 'Everthing is sold out. We can go home now', 'is sold out' is describing the state of the 'everything' while 'Everything was sold out yesterday' is describing the action of the goods being sold out, right?