Q: Dear Shmuel, I have a few things I want to send from my parents' home in Florida. It is less than the minimum the shipping companies require - Can I share a lift with someone?

A: Sharing a lift is something that we, as officially licensed customs clearing brokers, cannot get involved in. When we go to Customs and say this paperwork represents the goods of Moshe Ploni, we cannot know that Joan Doe's things are also in this lift.
That being said, what we don't know, we don't know.
Do people share lifts? Sure, all the time.
As long as all items are being declared and customs duties are being paid, there is no real ethical dilemma. You just have to make sure you know up front what you and your partner are paying and how you are dividing it up - including unplanned expenses. The classical example is the cost of a customs/security inspection. (Perhaps I am na ve in assuming you and your partner know all expenses up front - this is something you have every right to know - in advance.) You will also want to work out, in advance, any extra charges for "second delivery" or "second pick up."
Keep in mind security issues if you are sharing a lift with someone you do not know - make sure you really know what your partner is shipping. Hidden guns and drugs will always mess up a lift experience.
The advantage of sharing a lift is saving on the one-time expenses and in case you have less than the minimum, not having to pay for unused space.
The real problem is when an oleh or toshav hozer brings in things for someone who is not entitled to a tax free import. This is an ethical problem as the law is very clear on who has to pay customs duties.
Finally, if your shipment is relatively small, don't overlook sending it via the Post Office. For small shipments - this is often the best route.
All the best,
Shmuel