you'll be protected through Paypal!
Not necessarily. PayPal Buyer Protection should cover you if a company or writer doesn't send you anything at all, if they miss your deadline significantly, or if you can show that substantial portions of the work were
flagrantly plagiarized (i.e. outright copy/paste vs. insufficiently or improperly referenced, which it probably won't cover). It also probably won't cover you at all if they send you a horribly-written, amateurish, nonsensical essay that is equally worthless to you, because PayPal won't get into or entertain any arguments about anything subjective, such as whether the work is "good" or "bad" or whether it's written at the appropriate academic level; they probably won't even consider certain kinds of objective arguments, such as whether the writing is grammatically correct or in strict compliance with specified referencing styles.
But paypal won't refund if its done in payments such as half down n half after receiving.
I'm not so sure about that. They certainly won't protect your first installment after you've paid the second; but I think they will protect you for any payment if the work provided (and related circumstances) fit all of the other protection criteria, such as I've outlined above. Once you pay for the second half, you're probably only eligible for protection for the second half.