Social proof works best when it's woven throughout the letter at points of hesitation, rather than confined to a single dedicated section.
Sprinkle Proof Near Bold Claims
A significant claim followed immediately by supporting evidence or a testimonial reduces the skepticism that claim would otherwise generate on its own.
Use Numbers as a Form of Proof Too
Statements like "joined by over 12,000 customers" function as social proof even without an individual testimonial attached.
Don't Let Proof Replace Your Own Argument
Social proof should reinforce a case you've already made clearly, not serve as a substitute for actually explaining why your offer is valuable.
Next step: Use the Sales Letter Writer to identify where in your draft letter social proof would reinforce a specific claim.