As one who has lived overseas for work several times, I can say that there are can be several issues.
First, other than the US Post Office, shipping is very expensive. It might cost over $50 to send 1 car.
Customs documentation is not hard to fill out, however, unless the package says gift with no value, the package often gets held up in a customs warehouse. At one point point my employer sent me a set of transparencies for a presentation that I was to give. They were held up by customs and I would have had to travel 50 miles each way to get them. There is also an issue that sometimes customs randomly opens a package, looks at what's inside, stuffs everything back into the box, and then just tapes it shut, without really repacking the item.
Unless you use the highest level of shipping, there's no tracking, so you really do not know if the package will arrive.
Having said that, we never had any major problems shipping anything overseas. All the birthday presents our relatives shipped the family arrived on time and in one piece (sort of). Even stuff like electronic components arrived.
Over the years I have found the US Mail International Priority Mail flat rate boxes work very well and usually arrive in Europe within 10 days.
My feeling would be if you ship, ship as a person, rather than as a firm and it will be below the customs radar.
Lad
PS Shipping back to the US is easy. You label the package "Used Toys and Household items" and US Customs clears it instantaneously. I sent quite a few trains back home this way after spending 6 month in Europe. (It probably did not hurt that I had a child with me and the trains were included in with boxes of Legos, etc.)