How about verifying a seller's paypal account on ebay? just by looking at the power seller thingy?

Let me decompose your question(s) into a few parts.

Firstly, powerseller status does not mean an identity is verified.  It's simply a track record of how much sales a particular seller does.

Secondly, if you want to do some verification on ebay, this is what you do.  It's a little known fact, but there are different types of seller accounts on eBay.  You can check to see if the account has Verified status - but this is rare, so even if it is not there, it doesn't mean much.  There is usually a tick symbol next to the eBay seller name.

This is what I recommend - if you are dealing with an eBay seller, prior to making payment, request for the seller's identity details via the eBay system.  Let me know if you need the link.  Basically, what eBay will do is that it will swap information between you and the seller - seller will get your buyer account information and you will get the seller's account information.  From this, you can tell if you are dealing with a P.O. Box, or a non-existent phone number, etc.

Hope it helps,
Playbook