How to measure the value of an offer: (Dream Outcome × Likelihood) ÷ (Time × Effort).
Alex Hormozi's framework from $100M Offers. The value of any offer is: the dream outcome the customer wants, times the likelihood they'll actually get it, divided by how long it takes and how much effort they have to put in. Maximize the top; minimize the bottom. Every 'grand slam' offer wins on all four variables.
Before writing a single line of copy, run your offer through the value equation. If any number is bad, fix the offer, not the copy. This is the quickest diagnostic I know for why an offer isn't selling.