Hi Elizabeth, it doesn't appear that you charge a deposit, so there isn't any option for you to charge for damages except requesting payment through a resolution request, and the guest would have to agree to pay the charges.
I have a number of listings and I've dealt with every kind of stain imaginable. If it's biological it should come out if it's treated correctly. If it's something like hair dye, it might be a bit tougher. Several posts have been written here about stains, and I think @Deborah even created a handy chart that you should be able to search the Community for. Personally, I consider stained linens and towels a cost of doing business and unless it was a result of a guest directly breaking a stated house rule, I personally wouldn't pursue payment. That's me, and you of course have to do what works for your own business. But the time/energy it takes to go through the process might not be worth it if you can easily replace a set of sheets. Only you can decide!