The issue is PayPal rules are arbitrary and a scammer is going to know how to use them to his advantage is both directions.

For example if a noob pays by gift using a PayPal account with a balance he likely is screwed.  
So never pay by gift.  I would also point out that too sending or receiving too many gift payments can get your account frozen or cause you to lose the ability to make gift payments.
This has nothing to do with "scams" and everything to do with the fact that PayPal doesn't get paid on gift payments.

Oh so if sending by gifts can be reversed, than receiving by gifts must be safe right?
No absolutely not.  A scammer is going to be more than willing to pay by gift using:
a) a hacked/stolen PayPal Account -> auto reverse you lose
b) Claiming his account was hacked/stolen -> auto reverse you lose
c) a $0 balance PayPal account (where tx is funded in realtime by CC) -> charge back on CC -> reverse on PayPal you lose.

PayPal requires complete and absolute trust because it can be used to scam both ways.  A scammer is going to know all the ins and outs and the sucker isn't.  So even if it looks "safe" you probably can get burned.
For example FastCash4Bitcoins uses PayPal payouts but you shouldn't use our service unless you already trust us.  If you can trust us with your coins you can trust our PayPal payouts are legit too.

Sadly no matter how many times this explained people seem to get scammed.

TL/DR:
Paying by gift to an untrusted persons = dangerous.
Accepting payment by gift from an untrsuted person = dangerous.