Why are there so many fraudulent sellers on here
eBay is what it is; eBay a jungle, where almost anyone can sell or pretend to be selling almost anything.
You might instead ask why so few buyers to read the clear warning eBay gives them in the user agreement, that eBay does not guarantee the quality of items sold here, or that itm descriptions will be truthful or accurate. eBay doesn't even guarantee that items for sale will be safe, legal - or even exist.
Buying from unknown sellers on eBay is NOT like buying from the shops or reputable online retailers. Would you have bought a high end phone from a shop that stated this??
You have to take responsibility for your decision to accept the risks of buying here - especially from unknown new sellers with zero feedback. You also need to understand that eBay's money back guarantee is not without loopholes (especially over disputed delivery) or a substitute for using common sense.
I'm glad you got your money back twice, and hopefully the same will be true for the third. I suggest that you think carefully before buying a fourth time. If you still choose to buy on eBay, do please minimise the risks by buying from a well established seller of phones with a solid history of good feedback.