So does the internet!!
Beyond that - it is the teacher's / parent's job to ensure that thier children are learning instead of cheating - not a Bool Store's, an internet auction site, a reseller, the government's or anybody else!
The teacher editions for all the textbooks currently used by public schools in my state are available in every university library that has a teacher education program. Ebay acts like they are protecting the answers to the SAT or GRE tests. The rationale for not selling these books is just ridiculous, in my opinion.