Are you prepared to bear the risks during transportation but have the seller organise and pay for transportation to the agreed place?
According to this proposal, if anything happens during the transportation, you will bear the risks.
However, it will not be you who will cover the transportation costs. It will be the seller. It will also be the seller who will organize the transportation.
You will only bear costs if anything happens to the cargo on its route.
I'm not totally sure I understand the meaning of this on a semantic level, but that's how it looks to me.
Why "organise" does not take "s" if it refers to "seller"?
"To have someone do something" is a construction that means roughly to cause someone to do something, to make someone do something. Or, closer to your case, to "give someone the responsibility of doing something":
This construction means "to give someone the responsibility to do something."
Dr. Smith had his nurse take the patient's temperature.
Please have your secretary fax me the information.
I had the mechanic check the brakes.
In your case, you could give the seller the responsibility to organize and pay for the transportation.