Selling a new treadmill, bought a couple of months ago. Didn't fit the dimensions, too big for our studio apartment. You can come and check it out, the condition is excellent
Never pay down a deposit in a bank account until you have met the seller, seen signed a purchase agreement.
No serious private advertisers ask for a down payment before you meet.
Receiving an email with an in-scanned ID does not mean that you have identified the sender. You do this on the spot, when you sign a purchase agreement.