I've had the new edition trick pulled in most textbooks I was assigned in university. In my calculus classes, the new edition would essentially consist of swapping around the homework assignment numbers and shuffling sections around to make it difficult for students to follow using older editions.
Fortunately, I had a calculus teacher who was sympathetic to students and at the beggining of every class would release a table showing what the equivalent page numbers were for each edition for that day's material, and a table with equivalent homework assignment numbers per edition at the end of class. This allowed students to use older, cheaper editions if they wished
The irony was that that course had the highest percentage students buying new textbooks of all the courses I took in university, because students felt the book maintained value by being re-usable year over year through the teacher's equivalency tables for each edition, and so could easily resell them at the course's end.