It's always going to depend on the nature of the relationship of the student and instructor, but in general - I don't think an instructor should feel beholden to reciprocate. Given that, the gift giver might not feel the same way as I do. LOL. However, if a teacher does choose to reciprocate, it might be wise to take whatever necessary precautions so as not to look "unfair" to the rest of the student body. Small gifts are good, home made (baked goods etc) is usually a good solution if possible. I try not to make the recipient feel guilty if they did not reciprocate.