If you email them a second time, a week later it's not badgering or bothering them. If they don't respond after that, then move on. Obviously they are unable or don't want to do the project. :/ (and not worth pondering over)
I've had instances where I have missed an email and people have emailed me saying "did you get my email about doing a commission?" Like I said before sometimes it hits spam box or sometimes with SO many emails, you miss some. It doesn't hurt to check up at least once. But yah, I can see checking several times about a possible commission can get "annoying," but they brought it upon themselves.
If the commissioner gave you info and started the process (minus doing a down payment), they really should get back to you ASAP. It's not right to leave people hanging that are interested in having you do a costume/wig for them. Plus, they gotta set up their own schedule for the product, so they'd be screwing themselves in the process too. It's a no win for anyone.