[Kalimac]

From the way the story is written, it doesn't seem like it was Sauron's idea - in fact he seems to have been fairly preoccupied with Gondor and Rohan and looked on hobbits as being rather like annoying flies - something to be dealt with later. Doubtless he would have gotten his revenge on the Shire in time, if he had had the chance, but it wouldn't have been like that. Saruman began corrupting the Shire while he was still Sauron's agent, but it was definitely a sort of private side-enterprise for him (as quite a few other things were - would Sauron really have let Saruman have the long-distance run of the Shire for that long without interfering directly?) The fact that Saruman made for the Shire after he had left Orthanc and was in bad favor with Sauron, and the fact that he considered the Shire a good hiding-place for him would show that Sauron couldn't have been terribly interested in it (since the Ring-bearer was long gone), as of early March of that year.

OTOH you could say it was Sauron's fault ultimately for corrupting Saruman and turning him into a tool who would do things like that which were very much after the spirit of Sauron himself. But Saruman was always a weak imitation of Sauron - Sauron would never have wasted time bullying hobbits with Shirriffs and taking pipeweed, he would have gassed them all in the first day and turned the Shire into a waste that even Sam's box might not have been able to replenish. We can safely credit Saruman for this particular corner of destruction.