I bought a dvd for the first time from canada and when it came though my letterbox it had a green sticker on it saying customs can open this envople.
Does this mean it has been opend or would there be another sticker on it saying so?

All I know is they have every right to open any parcel.

If the parcel is under about £18, they charge you nothing. They are sometimes very lenient.

Just don't go importing any dodgy movies, if you know what I mean.

whenever you order, choose the gift option (i know amazon lets you do this). I've been ordering stuff from amazon (i'm in canada) and if the package is marked 'gift', itgoes thru customs and they don't bother with it unless its valued over 60$. The good thing is that when you choose the gift option, amazon writes the value as '0', so no customs. I recently placed an order for 270$ US and i didn't have to pay customs on it