I current list an item on Ebay which is my camera that cost $1700aud. For less than an hour I received a message about a buyer and offer $100 extra. Most of the time they would offer less of the price. The price would attract the seller. But definetly do not response especially if they want an offer and messages you and not directly to ebay. This would be the idea to scam you. Never agree on a fake paypal emails that you received and the amount will never reflect on your paypal account. It is safer if the item was officially bought through ebay and have the money pending on paypal.
Not sure of your question as you appear to have answered your own concerns well enough, but any direct contact will be picked up by Ebay and both you and the other party could well be given an Ebay holiday. Best to not even communicate with them.
