Define
A conditional contract: if you do this, you get that. The sentence can be tested against the reader's own case.
Mechanism
Contingent claim. 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 doing the work.
Don't
The condition is vague, or the result cannot be checked. An untestable if-then is a wish.
Copy skeleton
If you [ACTION / CONDITION], then [RESULT] within [TIME], or [CONSEQUENCE / GUARANTEE]. [ASK]
Gulf note
Write the if and the then in the register the buyer already uses. Name who honors the clause. A promise without a named party is decoration.
Rights-cleared examples
Charles Atlas 'Dynamic Tension' ad, Weird Tales September 1941
Charles Atlas 'Insult that made a man out of Mac' comic ad page, The Black Terror #12 p.36
Charles Atlas comic-strip ad, Slave Girl Comics #2 p.51
-his sore throat may be yours tomorrow!
A Frank Confession" Gillette statement ad, The New York Times 15 Feb 1932
Again She Orders - 'A Chicken Salad, Please'" - Book of Etiquette (Screenland, March 1924)
An Old Man at Fifty, A Young Man at Seventy" by V. O. Schwab, Sanford Bennett book ad, The Outlook May 29, 1918 (leaf 32)
Bell Telephone System ad featuring clown Emmett Kelly, American Legion Magazine September 1949
Charles Leroux flyer
De Stijl advertisement page: Maatschappij tot Verzekering van Uitgesloten Risico's
Do You Make These Mistakes in English?" - Sherwin Cody School of English (Mid-Week Pictorial, Dec 7 1929)
Do You Make These Mistakes in English?" Sherwin Cody School ad, The Mentor January 1922 (leaf 41)