She said 90% of lost international packages are because of poorly written customs forms. If you write clearly on the forms there shouldn't be any issue.
I try to avoid having to manually fill out the USPS Customs forms, as the USPS clerk has to enter all the information manually, which makes for a slow process. The forms are simple, though, and you can use peel and stick address labels in lieu of hand writing the addresses, too, which helps a lot.
With eBay's system, it's three clicks and done for International labels.