This is called a wash trade, and it is used to make something look like it has more interest than it does in the hopes someone else will look at the trade volum

This is called a wash trade, and it is used to make something look like it has more interest than it does in the hopes someone else will look at the trade volume and bite, in which case the trap is sprung, and no one else will be interested in a purchase off of the duped purchaser.