Keeping chickens can be as complicated or as uncomplicated as you want it to be. I have had chickens for many years, and very few of them have eaten out of my hand. That does not mean they have not been handled properly, it just means that those particular birds were not raised to be pets. Even if the guy you bought them from had handled them, they very likely would still be skittish around you. Chickens are prey animals. They instinctively run or shy away from anything new. They do no know you. They are in a new place, different surroundings. Chickens don't do change well. They will be more comfortable around you with time. If you just sit in the pen with them quietly, and don't make any moves toward them, they will learn that you don't mean to harm them. Bring some treats with you and just drop them by your feet. Eventually they'l come closer. They don't necessarily need a "health diet". Just regular feed will be fine. I'm not sure where you read that chickens like to roll in mud, but I've not experienced that. The most important thing to do is relax and enjoy your flock. As long as they have food, water, shelter from the elements and a secure place to sleep at night, they'll be fine.
