There could be a lot of reasons. Some companies are famous for quoting incredibly low prices on the telephone, but when the customer goes in for service they find out that other parts are required and that tax and labor was not included. Some companies quote low prices because they use inferior aftermarket glass and cheap inexperienced labor. Unfortunately, most people don’t know the difference or don’t understand the safety implications and they make their decision solely on price. Don’t be fooled by gimmicks and giveaways. The old adage applies: “If it sounds too good to be true, it probably is.”