For us, we will NEVER do a wall project without first testing adhesion. To do this all you need is the appropriate spring scale (see 3M rest kit). You then need the various materials you are considering for the project. Make you strips and go test the wall.
If you client is far away, hire a company in that area that knows what they are doing to do the test and installation.
You HAVE to explain this to the client! YOU are the professional and had better know what you are doing. Just being able to print and install a graphic is not enough. Educate yourself, your staff and your clients.
Doing stuff with the cheapest materials you can purchase!? Well the old adage applies, you get what you pay for!