The bar is not quite that high. I recall hearing about a case where the cops suspected someone so they sent a fair amount of advertisements for an illegal product to their house. The defense basically said, they did not bite the first time or the second, but after a while curiosity got the best of them. The important thing to note is they passed up several opportunity's before trying to commit the crime.
In this case, as long as the cops don't actively advertise people probably can't use the entrapment defense. But, if they setup a large ad-words account then in theory that's a problem.
However, If the jury finds that the defendant was predisposed to commit the crime that he committed, the defendant will not be allowed to use the entrapment defense, no matter how extensive police participation was in inducing the defendant to commit the crime on this particular occasion. So, if the prosecution demonstrates someone is a habitual drug user then the cops can advertise freely. But, if they cops advertise and someone that's been clean for a few months/years calls them up that's a gray area that depends on the jury's interpretation.