Why do you think my company has a strict gift policy? I obviously am not going to favor a supplier because they give me a $10 gift. The problem with gifts and such is that they grow into expectations. I used to be a customer engineer on an account in which the buyer expected us to take him to dinner at a particular restaurant each time. That company is a competitor of my current company, and I never liked it then, and I still remember how unfair it was.
As I said we give frequent gifts to our childrens' teachers. I think the biggest gift we give them though are our children ready to learn and give it their best shot. In classrooms in which fish are poisoned, computers are taken apart, and objects are thrown; my kids are always ready to learn.
I guess it comes down to an appearance of impropriety. When I was in school I always kept an arms length relationship with my teachers. After the grades are in the book, some have become close friends of mine.