PayPal

PayPal is running a special with 20% back when using their Pay in 4 option. So for example, I buy something for $600, am I billed $150 or they deduct $150 from my bank account associated with them every two weeks? Or do they put the $150 on my PayPal Credit card on a every two week schedule and I pay it on my own? Getting $120 back seems like a good deal so I want to make sure I am using this option correctly without paying interests. Thanks!

EDIT: Seems as if the consensus is that I either leave it alone all together and risk the $15 dispute fee down the road OR refund the disputed amount and ignore the outright request for the second $1500. Thoughts on which path is safest?

I really need some help here. Yesterday morning, I received $1,500 from a random person with the message that this was a Christmas present (it was obvious that it was not intended for me due to the message content). Around 7 hours later, I received another $1,500 from the same person with no message. I rarely use my PayPal account, so I honestly thought the notification emails were a scam themselves. The next day, I woke up to "You have received a case" with the information that "your buyer filed a case on this transaction for the following reason: the buyer stated that they were billed twice or billed incorrectly". The same user had also requested $1,500 just outright (presumably for the second $1,500 that isn't part of the dispute).

I call PayPal, explaining that this feels very much like a scam. The representative says that if I don't refund the amount in the dispute, there "is a high likelihood that I will be found in the wrong and have the amount taken, plus a $15 dispute fee". I read the user agreement that says, "When you receive a payment, you are liable to PayPal for the full amount of the payment sent to you plus any fees if the payment is later invalidated or reversed for any reason." This makes me extremely hesitant to do anything with this money. I'm not a seller on PayPal and am unsure if this payment was sent via friends/family or seller/buyer, but it seems the latter as the dispute references the term buyer and billing.

So, now I'm coming to you guys as someone who wouldn't think she'd be caught up in a scam as a young person, and who is very confused. What do I do? Nothing and eat the $15 dispute fee that may come as a result? I don't want to be out any amount of money, but would take the $15 dispute charge over losing potentially $3,000. Please help me!!!!

Edit: Yes, I spoke directly with PayPal by locating the number found on the app (not via a message sent on the app, but directly in the help center). However, I do agree that the rep's advice sounds a bit sketch which is why I'm here.