I've noticed lately that not responding seems to be the new method many people are using to opt out of simply saying "no." It used to happen more in my personal life. We've probably all sat on RSVPing to an event at some point in time. Now, it's happening more often in the business world. Professionals, even professional communicators, are choosing silence as a response.
Don't like the estimate you received? Just don't respond. Changed your mind about having that coffee meeting? Just don't return the emails. If relationships are paramount to business, why is this becoming acceptable? It feels disrespectful when someone won't respond to outreach -- especially if you had a relationship with the person prior to the issue.
If you have to decline someone's offer, whether personal or professional, just do it. Say it kindly, say it promptly...just say it. The tension created by making that person wait for a response or have to follow up is more damaging to your relationship than being straightforward. It's perfectly acceptable to tell another professional that plans have changed, that's outside of your budget or you're not able to assist them right now. This will help you maintain a positive reputation and give them the resolution they need to move on to the next opportunity.