Is it really more of a liability to pack my own boxes?

I'm looking for moving/shipping companies to send a couple of boxes of books & clothes from Australia to the USA (as I'm relocating). While requesting quotes, one company strongly suggested that I hire them to pack my things for me as apparently US Customs get suspicious if the boxes were packed by the individual mover (me, in this case) rather than by a professional. I haven't seen this mentioned anywhere else and the US Customs website hasn't addressed this. What's going on? [more inside]
posted by divabat on Jul 1, 2012 - 12 answers