It changes at one moment: when you buy something.
While you are watching
That somebody is watching — you are a number in the viewer count, nothing more.
Your display name, if you chat. The name on your profile, which is yours to set. How to change your name
Your display name if you are the top bidder, shown to the whole room as who is winning — not only to the seller. Can I bid without my name showing?
Not your address. Not your number. Not what you have bought elsewhere.
If you are watching signed out, they see a number and that is all. Can I watch without an account?
Once you buy
They get your name, your mobile number and your delivery address — because that is what putting a parcel in the post requires.
Attached to that order. Not your other orders, not your email, and never your payment details: the card does not reach the seller. Who can see my delivery address?
What they never see
Your maximum bid, if you set one. The room sees the current price; nobody sees the ceiling behind it.
What you bought from anybody else.
Your account history — strikes, disputes, how long you have been here.
What you see about them that they cannot hide
The reserve is theirs, not yours — it is never shown to buyers, so it cannot be moved during the bidding.
Their ratings, their returns policy and their dispatch time are all published before you buy, which is the asymmetry working in your favour.
Can they message you?
Only with a real connection: you bought from them, you talked before, you follow them, you bid on one of their items, or there is an offer between you. A store cannot pick a stranger and start writing. Can I message a buyer directly?
And a store that blocked you cannot then message you.
What the address may be used for
That order. Nothing else — not a list, not contact outside the order, not passed on. Using it otherwise is reportable. How to raise an issue
If you would rather give less
Pickup hands over no address at all; you get theirs instead. What is a pickup point?
Send it somewhere else — a workplace, a relative. The order stays yours, so the protections follow you rather than the doorstep.
More: who can see my delivery address, does Metzee sell my data, can I bid without my name showing.