After moving to a new area, I needed to find snowplowing for my driveway. I searched online and found a few decent looking websites for small business that do this, among other services. Only one offered an email address. I sent a message and got no reply.
A friend in the real estate business who works for a local office of one of the big franchises, had someone send a test inquiry about one of his listed properties. The inquiry didn't come to him as he expected it would. It came to another agent...who replied two months after the inquiry had been sent.
More times than I can remember, I have sent inquiries to local and national businesses, using email addresses on their web sites and sometimes web forms, indicating a desire to do business with them, and have received no reply.
I have left voicemail messages with contractors and others, requesting quotes or information, and received no reply. Some of them have big Yellow Pages ads. Why?
I'm not sure why you would publish an email address or a phone number, or even have a web site, if you don't make it a constant practice to respond to people who are interested in your business.
Even if business is good right now, it may not be tomorrow. The people you insult (and it is an insult) by not responding will not call you the next time they need work done. And they will not tell their friends about you, at least not in the way you would like.
The message is clear:
If you reply to inquiries -- potential customers -- you will stand out from the crowd. Even if you do not win that business, you will be remembered.