Maybe someone has mentioned this, but I didn't see it: surrender fees. Every shelter does not require a fee, but many do.
Yes, I was surprised that all the shelters around here have them, even if you are dropping off a stray you've found.
Sometimes, Animal Control (which typically has a "kill" shelter) will take them for free. That's a bit different from an Animal Rescue. I'd love it if euthanasia was provided free of charge through animal control. I know it is in some communities, but not most. It's not attractive, but at least it isn't cruel.