For their Buyer Protection Plan to work, they pretty much have to have access to seller's funds. If you never have a problem, they will never debit your account under this plan. Probably a small percentage of sellers create the need for this but with a company handling millions of auctions, it's a business necessity.

They have a reputation to maintain and if you have a defense against their debiting your account in reponse to a buyer's complaint, I'm betting they will give you the funds back. It may not be easy, but if you have a good reputation as a seller yourself, you don't have much to worry about.

ebay provides a great service. If you want to play their game, you play by their rules or play somewhere else. I'd sign the agreement.