One size doesn't fit all when you're talking about effective customer support. Certainly, clients with a rack down require a different type of response than a shared client who needs help receiving email on their smartphone. Most, but not all, clients understand that some issues take longer to resolve, like mitigating DDOS attacks.
Regardless, each and every client deserves the very best customer support, and communication is key to making that happen. Perception is important. If I perceive, as a client, that level 1&2 techs can't resolve simple live chat issues or keep you on hold for extended periods of time on phone support (without reassuring you from time to time that they're working on a solution), I'll probably become one of your customer churn statistics.
Complacency is a client killer too. You might think your customer service is outstanding, but are you asking your clients (on a regular basis) how they perceive your support? And if you do ask, do you follow up immediately on any issues?
I do agree with Romes that being upfront and truthful is paramount. If I even remotely sense that I'm being lied to or being put off, it raises red flags.
Put yourself in your client's shoes - not all of them are web hosting literate, while others often surprise you with just how much they do know about hosting plans, servers and troubleshooting procedures. Each and every one of your clients contribute to your success as a service provider, and a personal approach certainly works wonders versus a robotic response - across the board.