Its nice that its free, but its pretty lacking on logical things you need for it to work properly.
First, there is nowhere to set a minimum price. You can only set a "regular" price, which displays to the customer as the "suggested" price and acts as the minimum price they are allowed to offer. Pretty pointless if the customer cant enter a better price than what is suggested to them.
Second, if the customer enters anything less than the suggested price they get the message "Price must be higher than the minimum price". How do they know what the minimum is?
I guess this is good If you want to accept donations, as someone can put any amount in, saving you from having to create multiple listing at different denominations.
If you want to offer your customers the ability to haggle with you though, this is not the plugin for you.