The thing that bothers me about your story is that Paypal inherently has buyer-protection built right in. If the buyer sends you the money and you send a bad item, THEN the buyer can dispute the purchase. Paypal will refund the buyer's money and will then come after you. So your buyer's added layer of "freezing funds" for 3 days is unnecessary and puts ALL the risk on your shoulders. In this transaction, risk must be shared equally.
Sounds like you have trepidation on this deal so here are the steps I would take.
* Tell the buyer that if he's not willing to send the funds in a traditional Paypal manner (withOUT a hold), he can piss off. Assuming he's good with those terms....
* WELL DOCUMENT the condition of the Inspire one with VIDEO. Make sure you show the Inspire 1 flying about, doing what it's designed to do. Show that the batteries work, the controller works, the bird boots up with no errors and on and on. Cover every nook and cranny of the bird, the controller, batteries, accessories, etc. Be sure to highlight any distinguishing marks (like scratches) so he can't claim you sent a different bird. Diligence is your best friend.
* Post the video to YouTube and share the link with your buyer. Let him know that this is the video you will share with Paypal should a dispute arise.
* Cite that the video is proof the item you are sending is in good working order.
You're not selling a $200 battery. Your buyer is investing thousands. So an elevated level of diligence on your part is to be expected.
The drone world is a very high-tech world. If you lack the ability to shoot video and upload it to YouTube or Vimeo, then you shouldn't have purchased a drone in the first place.
I've done thousands of purchases via Paypal for as much as $3,000. Paypal is in the BUYER's corner. Therefore, this extra layer of holding back funds is not necessary.
Good luck.
D