To .ch: I have never heard of pple nixing a shidduch because the bochur has smoked sometime in the past. I think that if someone was able to overcome the addiction of smoking, that shows incredible strength of character.
However, I have heard of cases where the guy claims that he doesn’t smoke or “gave up smoking”, and then after marriage resumes smoking, so that the wife who did not want to marry a smoker is now married to a smoker. So there are both perspectives to take into acct.
But your recommendation of finding out [from reliable sources!] that he has stopped for a year is a good one, IMO.