PostNet pricing - huge variances amongst branches

PostNet approves of one branch (Midrand) charging R60 for the same product for which another branch (Groenkloof) charges R25. (A2 colour print). Although their website states that shops are individually owned and operated and that products, services and pricing may vary, surely there should be some kind of pricing guidance which does not allow a 240% variance. What is then the purpose of franchising? Surely one should be able to expect similar products at similar prices.