Q: What are some questions I should ask a DJ/entertainment company I'm considering?
A: The first questions you should ask should be, "How much experience do you have, and what do those experiences include?" While longevity does not always equate to talent, someone who has been doing big events like weddings for years will likely be more reliable than someone who has only worked a handful of them.
An extremely helpful question is, "Do you have any samples we can see and/or listen to?" Between sites like Mixcloud, Soundcloud, YouTube, and others, there are a plethora of options for DJs to post sets for potential clients to listen to. Do they play the entirety of every song and then simply fade out at the end? Do they go scratch-happy on every track? Do they use annoying sound effects? (You just made the 'Bwrr Bwrr Bwrr BWRR!' horn noise, didn't you?) Any DJ can talk about what they can and will do, but can they prove it?
Another helpful question is to ask, "What does the average (insert event) look like to you?" In other words, if they had a blank canvas, how would they put the night together? What songs are they playing at cocktail hour, when doors open, during dance sets, during dinner, etc.? What kind of timeline do they think works best and why? How they answer can provide insight into how experienced they really are and can even help give you some ideas for your big day.
Finally, at some point in the conversation, you should ask some variation of, "Are you the person who will be working my event/Will I get to meet the person who will be working my event?" As a single-operation company, I handle everything myself, so you can be assured I will be the person working your event. However, multi-operation companies have several employees on their roster. While this comes in handy when getting multiple inquiries for the same date and/or filling in during an emergency, some companies will randomly assign events without the clients and talent ever meeting until the day of the event.