Grubby feeties, yes. Dirty backsides? Not so much. Now, a soggy Silkie - that is one sorry sight!
Over the years, I have had some really sweet Bantam Cochins, and I have had some that were real snots! We have a couple of hens now that can be picked up and carried around (they will even eat out of your hand while being held), and a roo that has to have his butt kicked every so often to remind him of his place. I'm trying not to let the cranky ones contribute to the gene pool, so "Goldy" (aka "Stupid Chicken") will not father any eggs that I will hatch, even though he is a beautiful bird. My daughter raised Goldy, so she was pretty upset the first time he attacked her. She's old enough that she got over it, and has turned the tables on him many times since. Oddly, she is really fond of the little monster!
My opinion is that it would be best if you can see the parents, kinda like what they say about puppies. While you can't be sure that chicks from laid-back, friendly chickens will be as sweet as their parents when they grow up, aggressive birds do tend to pass on their fiercer natures to their offspring.