Yes, it is true. Your appearance does matter. You might think that you will look more authentic in informal clothes because you will feel more natural. That's a misconception. You are not dressing just for yourself, but especially for your audience. If you wear the "boring" suit, the investor will not have to think about your inability to chose clothes throughout your presentation.
Lack of eye contact
When you talk about what you would like to get from the investor, you should not look to the wall or on the screen with your presentation. Look in his eyes directly. It will show you are self-confident, open and trustworthy.
Too much information on your slides
The investor should pay most of his attention to what you are saying, no to what can you cram into one slide. Your slides should include only a few words or visuals to highlight what you will talk about. Rehearse your presentation without any slides.
Telling a wrong story
Investors want to hear a simple story presenting your plan so that they can remember it. Your task is to tell your story from the investor's perspective - cash flow, growth potential, industry, clients . If you speak too quickly or present too much technical details nobody understands, you will fail.
Jokes at the expense of the investor
Be very careful of your nervousness. Any jokes used as icebreakers can easily backfire on you. It is definitely not advisable to say something like: "If you do not have 5,000,000 for me, do not even bother."
Too flashy presentation
You certainly want to get the attention of your audience right from the beginning of your speech. This does, however, not mean that you should invade the stage and start screaming or waving your arms. Just the fact that a potential investor came to listen to you, is a sign of his attention. The aim of a presentation to investors is not to entertain but to inform.