we do not share your data with anyone and there are many ways to control the visibility and storage life of your data here.
but the internet is a public space and you should always assume your data could be compromised.
be smart with your password, use tor or a vpn, and use pgp for sensitive communications.
no, unless you have a relationship established and even then I would hesitate.
to me, communication is the key here. I can handle any problem if the seller let's me know what is going on from their end→