Need to be handled and used to humans everyday. Its not always aggression, most of the time they are bored and when they see a hand they usually just want to play fight and they play rough!! If you know you cant get to them everyday make sure you have plenty of things in their enclosure that they can explore. Pipes, tennis balls etc.
I got a jills a few months ago given to me that the original owner swore it was curst and was wicked... turned out it spent most of its time in a in a rabbit hutch with noting to keep it occupied and never handled, well only handled when it was used for workin