From memory my old boss said NZ customs wants the machines really clean.
Every Country that I know of wants the machines ultra clean.
They did not want invasive species. Even small insects/bugs can be an issue.
Speaking for Canada, usually if the machine was washed, but there's still debris in hidden spots like the undercarriage, belly pan, Customs will have the machine cleaned again at the expense of the importer.
If the machine was not washed at all, it will likely be sent back to the exporter at their expense.
If the exporter/importer do frequent transactions, and everytime the machine is dirty, it will be sent back at the expense of the exporter.
After seeing the devastation that invasive species can do, I think its a good idea.
Just make sure the exporter cleans the machine in and out, and gets all the hard to reach areas covered.