If the coach is owned by PPL, then ask them to fix the problem and then deal on the coach. Find someone there who knows something about the problem and work with them to get the shaking problem solved. You shouldn't have to resolve the issue unless you are getting SUCH A DEAL that you want to take a flier on fixing it yourself. All of the suggestions here are great and you can have them in your arsenal when you next talk with PPL, but they should MAKE IT RIGHT before you buy.
That's how I see it. Good luck