How to find buyers for ERC20 tokens?

⚠ n00b alert ⚠

I see some tokens that have 0$ value and not listed on any exchange, and still being traded.

How are these people finding each other and trading?

Is there any way to put ERC20 tokens up for sale and see if anyone is willing to buy?

For example: https://etherscan.io/token/0x2df43e6826cf24bb844cc78611b0036eea3671b4

Also, they are paying substantial transaction fees (Gas) for these worthless tokens?!

Could anyone please explain how is that justifiable?