Jokes at the clients' expense

http://theoatmeal.com/comics/design_hell
^ This. Is. Hilarious!

And completely true for interior design as well as web design. I have learned two things that a designer must know in order to avoid this situation:

1. The designer must gain the client's trust and confidence. If your client does not trust your design abilities and intuition, they will feel the need to take over. This can be disastrous.

2. The designer must know how and when to say, "No," and occasionally, "Absolutely not. You are completely incorrect/misinformed." It takes confidence, but is necessary.