How to find a good Dj?

Hello everyone! I am reaching out to get some advice on how to find a good DJ Originally we wanted a band, but after we discussed what was the most important to us and where we wanted to spend money... The photographer won. Thats not to say music and throwing a good party aren't extremely important to us. In fact we are kind of known for the parties we throw, and want to make sure not only do our guest enjoy themselves but us as well. If anyone has any suggestions on questions to ask, features that would be good to look for, what a good price point is for a four hour reception, and anyone local in Maryland that has any specific suggestions would be helpful. One of the issue that concerns me is just about anyone can be a DJ with technology advancing the way it has, how can I tell if what I am paying for is worth the money? What other roles beside playing music and announcing should a DJ preform? Any help would be great!!!