As someone who works in taste, people tend to overestimate their tasting abilities. Alcohol free beer, meatless snacks, etc. When presented without focusing attention to taste, people generally don’t notice.
If you give both options and are forward about it they will be 50% correct in discerning the ‘alternative’. Realization comes more clearly in the absence of physiological change (no inebriation, no caffeine effect).
However if people do find out you’re cheating them you can sell legit product all day, but people will still doubt you. So don’t expect long term business.