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The present research tested the hypothesis that an internal motivation to change is elaborated as an external constraint and is less predictive of change when the source is expert than when it is non-expert. In two studies, smokers were categorized as either dissatisfied or moderately satisfied according to their degree of dissatisfaction with their image as smokers (i.e., internal motivation to change). They were then exposed to an antismoking argument attributed either to an expert or to a non-expert source. Compared to moderately satisfied smokers, dissatisfied smokers perceived the source as making less effort to convince them (Study 1, N = 43), and as being less disrespectful (Study 2, N = 81), but this pattern was significant only for the non-expert source. Study 2 also showed that experts had more influence on intention to quit smoking among moderately satisfied smokers, whereas non-experts had more influence among dissatisfied smokers.