Yes, vaccines is a good one - they should require proof.
My daycare lady also conducted an interview with Thor where she watched him interact with different dogs and even told me which days would have the best mix of dogs for him to play with, based on his personality. I came in telling her that Thor is undersocialized, so I wasn't sure if it was standard or not.
Daycare can be a great option for dogs, just make sure it's a place with trained people. I took Thor to another daycare for a while, and while everyone was very nice and loved dogs, I don't think they fully realized his stress levels while he was there. He was always very tense when I picked him up. When I get him back from this new place, he's always very hungry and ready for a nap.
