Is this a scam (amazon.com)?

I'm selling my new iphone 5 16gb and this is what i got as a message from someone.

Her: I want to make purchase of your item but i would like to know the condition before i make purchase mail me back on amjphail at yahoocom

me: the condition is new.like, the wrapper isn't even off.

her: Thanks so much for being sincere, the item is for my colleague as a gift but she's currently on vacation so i want you to help me post it to her, i'll add $80 for the postage, send me the invoice of the total cost through PayPal to amjphail@yahoo.com so i can transfer the money as soon as possible.

SCAM

ONLY a scammer asks for MORE money. You do not send them any invoice - they pay through Amazon.com's checkout page

This is a Nigerian scam

DO NOT reply for any reason. They will pay, have you send to their "friend" then file a chargeback with Paypal claiming their account was hacked and there's an unknown transaction. Paypal contacts you asking for proof of delivery to the buyer's verified address. You won't have this as you sent to their "friend" and Paypal refunds the buyer's money out of your account and their accomplice resells the iphone for cash and splits the profits with the buyer

This is one of the most common scams online

NEVER accept any offsite payments and NEVER ship anywhere but the buyer's verified address which you verify by calling Paypal before you send anything.