How as sellers are we protected from buyers who take advantage of the system and rob us blind?

[makeuprules2015]

I have been selling on eBay for years and sell authentic beauty products, I work so hard to please my buyers for positive feedback and have been in the past and just recently been taken advantage of because the system fails to protect us buyers.  I find that the system fails us sellers who keep eBay alive and we can do nothing but cough up the bill.  Some buyers know the system well and they take advantage of honest sellers like myself and use threats to post negative feedback and ruining my reputation on line and where I shop to purchase the items I sell.  

Buyers lie and say that the item they received has been tampered with or no longer sealed although I know for certain I took all the necessary precaution to ensure they recieve the item in perfect condition. Who is to say that the buyer dropped the item then say that it arrived that way especially since I received their email days after delivery or maybe that they have changed the identical item for an exchange that they previously bought elswhere? Other times the buyer actually changed the contents of the perfume and returned it to me demanding their money back because the item they claim the item was fake and I know for certain it was genuine. 

In the end, we sellers have lost a lot of money and time to people dishonest people like this and make it difficult for me to trust any buyer in the future. How is eBay or PayPal protecting us from FRAUDULENT BUYERS?

It is so disheartening to be treated so unfairly and feel so low and at time I wonder why I even bother.

Is there anyone out there that can tell me I'm not alone?