In many cases - like tails and ears - I don't offer WIPs because I have sufficient photos of end products so customers/commissioners are aware of what their final product will look like. Even with custom-colors on small pieces, I don't share WIPs, since I have a consistent style with them and it's easy to picture what it will look like. I haven't really had any issues with this.
When it comes to a full suit, particularly heads, I'm not really sure where to stand with how many WIP photos to provide. The problem lies in that many times, when a customer commissions a fursuit, it is because they have not built their own or have not attempted to build their own. Because of this, they may not be familiar with some stages of construction, and will nit-pick things that really aren't going to be an issue. An example being, say, I finish the foam work and they get concerned because it's not entirely smooth, something that won't matter once the head is covered in fur. Or wondering why there are two or more colors of foam on the head when again, covering it in fur means it won't be a problem.
On the other hand, I've provided some customers with extensive WIP photos and I get absolutely no feedback, in one case the customer didn't express their dislike of some features until they received the finished product (despite their seeing several WIPs from the very early stages, they chose not to tell me to correct anything, all the while saying "Looking good!") and in another case, a customer was actually present while I was sculpting, directed me in the shape of the head as he wanted it (despite my expressing reluctance to make the head in that particular shape) and then was frustrated when the final product didn't look like the species he wanted it to be.
I personally am inclined to work from a customer's reference artwork and try to make my costumes reflect the artwork as best as I can, I don't do a generic "style" for my costumes, so everything I do is basically starting over from scratch. I don't have general templates I work from, so when it comes to heads and full costumes, it's hard for a customer to tell what their finished product will look like because I can't really just say, "It'll look like your reference artwork." At the same time, I don't want to be overly nit-picked, have a customer tell me to make changes that might not be appropriate and cause the costume to come out looking poorly in the end.
If you are a fursuit maker, how often do you offer WIPs, and how many of you take active criticism from your customers on WIP photos at various stages of the head sculpt? Obviously I want the products to turn out similar to the reference artwork, but at the same time I think there's too much potential for ambiguity if a customer requests adjustments that might not be in the best interest of their costume design, especially if it's not shown on their reference images that I'm working from.
Additionally, what sort(s) of things can I adjust in my ToS regarding this? (current ToS can be seen here: http://www.etsy.com/shop/adorablefoxie/policy ) I have had customers that say, "You know what you're doing, don't worry about WIPs," but then I have other instances where I feel like I'm just the hands, and they're trying to do the work for me, if that makes any sense. What would you guys do in these sorts of situations?