Having bought stuff for the business from different suppliers in the US and in Europe, I find that generally, the stuff coming from Europe (at least so far) Customs doesn't even look at. Maybe its because its not at the volume that stuff from the US is, so they don't bother with it, or what.
Now stuff coming from the US, they catch maybe 1 out of every 6 or 7 boxes. Literally I have had orders of 7 boxes of stuff coming from a supplier in the US, and only one of them will have a customs sticker on it. However I haven't found that the boxes are being delayed any by it. As with the above said order, I got 5 of the 7 boxes on a Monday, one out of those five were hit with customs, and the other 2 boxes showed up on Tuesday, neither hit with customs.
I think it all depends on if customs opens your box or not maybe. If the value on the box is clearly marked, I think they just make up their customs slip, slap it on, charging you the proper amount of tax and/or duty, tack on their pound of flesh of $5 for doing their job in the first place, and then send it back out into the postal system.
For the most part, customs officials are located at the postal porcessing facilities anyway, so when a parcel comes through, and has to go to customs, it just goes down to customs, they assess their taxes, and send it back up to regular processing.
Now if they decide to open it and check the contents, then that is a whole new ball game.
The one thing I have notices lately though is that when they do catch one of my boxes, they convert the US currency to CDN currency, which is normal, however lately instead of charging me the usual 14% HST on the box, they have only been charging me the 6% GST on the box. Not that I am complaining, and either way, I can claim it all back when it comes tax time, but just wondering why they changed it. At first I thought it was a mistake, but then all of them that get caught now only have 6% GST on them. I am in New Brunswick, and last I checked we have a 14% HST here.