Web based

Web-based so it's viewable anywhere, anytime on any device
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Intelligent

Never include the price in the email. Always give it it's own section in the proposal itself.
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Stunning

The first thing they see when they open it should "WOW" them.
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Personal

Your introduction should be personally written for them and address their real problem.
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Descriptive

It should describe exactly what you're going to do for them.
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Socially Proofed

It should include undeniable proof from previous clients that you can do what you say you can do.
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Visually Impressive

Attractive and relevant imagery.
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Clear and Concise

Pricing should be clear and easy to understand.
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Signable Online

They should be able to sign it online.
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Sent within 48 hours

It should be sent to your client while it's fresh in their mind.
I'm ready to sign up