The only benefit GSP has is to seller, they are covered if the package are lost or damaged. Seller loses nothing but IMO it's just for the lazy seller who doesn't give a f*ck if a rare MISB Cotton arrives intact or if the idiot drones ripped the box open and shipped just the game to save money.
I wouldn't count on that. I recently shipped a statue via GSP and it arrived slightly damaged due to shipping. The buyer filed for a refund, even though i don't offer refunds on collectibles and vintage stuff. ebay/paypal immediately rips the cash from my account and then asks for me to answer some questions. then they say if it is damaged in shipping to let them know. i did so, and the didn't give a sh!t. got an email stating they "sided with the buyer" and that i had to refund his money, plus pay for the return shipping!
Ebay is all about the buyers, not the sellers.