How I Improved My Memory in One Evening - The Amazing Experience of Victor Jones" (Judge, Aug 24 1918)
The pattern
This still is filed under If-then promise.
Define
A conditional contract: if you do this, you get that. The sentence can be tested against the reader's own case.
Mechanism
Specificity does the persuading. The if names the action. The then names the outcome. Hedging kills it.
Verdict
We can name both the action and the result without adjectives
Why it works
The ad is written as first-person reportage with a byline at the end, so it borrows the reading contract of an article rather than an advertisement, and the opening is overheard dialogue mid-scene which starts the reader inside a story with no preamble. The proof is dramatised before it is claimed: you watch Roth name sixty strangers before anyone asks you to believe anything. Then the objection the reader is forming, that is fine for you, you have given years to it, is spoken aloud by the narrator and answered in dialogue, which is far harder to resist than a pre-empted objection in the advertiser's own voice. The close is pure risk transfer, examine it, return in five days, owe nothing, so the coupon commits the reader to nothing but curiosity.
Steal this when
You are selling a skill, course or method where the buyer secretly believes talent is innate. Dramatise a practitioner doing the impossible thing in front of a witness, have the witness raise the reader's own objection out loud, then let the expert answer it and offer free examination.