P2P meaning Peer-2-peer or could be referred to as connoted by OP as person 2 person, is one of the most discrete way to transact cryptos without government intervention within a government crypto restricted territory. It's basically a trade between two persons but at times, there is either a third party in the trading scheme. These includes;

1. Direct p2p
This involves you directly transacting with your buyer or seller which ever position you occupy in course of the transaction and

2. Indirect p2p
This involves the use of a third party which could either be an escrow site or a trusted member/user to serve as an escrow

Challenges of both processes

1. Direct p2p
* Looking for a buyer/seller
* The issue of trust on the other party to deliver as agreed
* The issue of fair price

2. Indirect p2p
Using a member as escrow
* The main issue here is the issue of trust on the user serving as escrow
Using an escrow site
* The site is more susceptible to phishing attacks and hacks
* There could be delayed transactions due to site maintenance and breakdown
* The issue of withdrawal limits and sometimes
* The issue of KYC

It is a thing of interest to note that, the p2p system of trading is an added advantage to all especially those in crypto restricted territory because, it makes you stay anonymous to authorities and also, the bases of your business transaction with the other party remains secret while your account grows in fiat and coin equivalent.