Besides price, is there a way to distinguish quality from lesser quality materials? Is there a "better" way to attach hair or limbs?
Most people that sell them use basically the same materials. It should be stuffed with wool, with cotton interlock knit for the skin, the hair should also be wool yarn. I've seen some that have the limbs attached with buttons, so the doll is jointed, but mostly they are just rag doll style. I like hair that has been attached with a crochet cap, because then there aren't any bald spots.
Do kids prefer them over other dolls? obviously there will be varied answers to this question, but I'm hoping to hear others' experiences.
I have made 2 dolls for my son, and he loves them. I have also sold a few, and had good responses (I'm not selling any at the moment, so this isn't a plug). I think they are a lot nicer than dolls with hard heads, because they are more cuddly. Plus the hair is so nice and soft, and they are all natural materials. And I like that they don't have "made up'" faces. I prefer the ones with the simple mouth, rather than the smiling mouth.
Do they tend to be durable? And as a child's toy, and likely to be dirty, can you wash them?
The one I made for my son has held up very well. And he is pretty rough with it. BUT they do get dirty, like any doll. Weir Dolls where I got the kit to make my first one says (if I remember correctly) to submerge the doll in cold water and gently scrub the skin with a toothbrush. I've had pretty good results with that when Jupee (his doll) started to look like a coal miner from being outside with my son.
When I'm asking a crafter about her dolls, are there specific things I should ask about?
You could ask to see a picture of the doll front and back without its clothes on. I think that would give you an idea of the craftsmanship of the doll. Check the reviews, check her return policy.
I have to put in a plug for making your own, it's much cheaper, and while it's work, it's worth it to have made it yourself. You can buy a kit from Weir Dolls, that's where I got mine.