We don't take Yoda to a day care now, but we would definitely ask if there is a section only for smaller dogs. I'm sure lots of smaller dog owners wouldn't want their dogs playing around with big Great Danes all day. Right after that, I'd ask about safety and that to make sure they don't slip out accidentally (double doors or double fences, etc). And if there's any fun activities or field trips they get to go on... Not sure if places do that, but I think some MAY have field trips? I forget...
There's definitely a market for doggy day cares around Seattle, I think I know of at least two within a few miles of my house!