Reviews help businesses demonstrate past work and show credibility from their customer base. If you can't find any online, try to request a reference, even though most businesses should have locations to collect reviews. I personally use a mix between VIDEO TESTIMONIALS, GOOGLE REVIEWS, AND YELP REVIEWS.
I understand some do not like speaking over the phone and prefer email exchange which is totally fine. However, maybe attempt a phone call as it will help answer any concerns faster and help the magician better understand your event. The main reason I personally request a phone call is because you will get to feel how you both bond. At the end of the day you want to work with someone you trust and and feel comfortable with right?
Asking an open ended question in an email like "How much?" will just lead us to asking more questions. You can help the speed of the booking process by adding as much details as you can about your event like number of guests, event location, and event details like venue information.
The more details you can leave the better it is for us to quickly offer an estimated rate. Just keep in mind there is no such thing as a "going rate" for entertainers as we all have different backgrounds and experience. Expect to get a range of prices.
Get as much details about your event as it helps us understand what we may be working with. Every magician is different so expect a variety of rates as the experience and work history of every magician varies. At the end of the day we are all people and in my opinion find someone you feel comfortable with and that you trust. May your next event be filled with great magic!