Welcome, I could as a very satisfied user be evangelistic but if you look in Auctiva's 'About Us' section or glance at other posts you will see why it is free.
Auctiva has no trial period, Sellethon does on their statistics tool but this is not esential but can be useful.
Fees, in the future, who knows, Auctiva's CEO does not intend to at present, see recent posts by 'Auctiva Jeff' for confirmation.