I come across bobbleheads all the time with major to minor damage and/or defects. I've had a few people ask me how to judge a bobblehead in something less than excellent condition. There are so many variables that go into the value of the bobblehead so its really difficult to put a number or value on something without seeing the actual bobblehead.
I look at overall condition of the bobblehead first. Are there chips and/or cracks or pieces missing? Usually you'll find chips on the neck, ears or cap. Sometimes there are extra curricular items (more than just the player/person) such as a bat, ball, glove, etc. Depending on the manufacturer, some are made better than others. All of those things definitely have a negative impact on the value.
Secondly, I'll look for excess paint, chipped paint or anything to that degree. Most of the bobbleheads are hand painted, so the paint jobs can be a little spotty. I've had plenty of bobbleheads with a dribble of paint where it shouldn't have been. To a serious collector this probably decreases the value. Chipped paint certainly decreases the value.
Next, if its an SGA bobblehead, a ticket and/or COA card will only increase the value. Many collectors will only buy bobbleheads with COAs and tickets. While others (like me) aren't set on needing them for their collection - if I get them, great. But if I find something I like and its in my price range - card/ticket does not matter.
Tilted head. Whats that you ask? We've all seen them - a bobblehead with its head way off center. Personally these don't worry me too much. Unless the head is way off base. Does it affect the value? I'd say (again, unless its significant) it shouldn't.
Bobbleheads are massed produced and because of that not many of them are in pristine condition - where everything is absolutely perfect. Those tiny defects shouldn't stop you from buying it. Just be careful (and inquisitive) when looking to purchase one. Below is a picture of random "defects" I've come across. Some major, some minor. Ultimately its up to you to determine what is major and what is minor.