I didn't have any problems, only one lady, she used to have a rubbish wfp'er. And I proved her wrong, she couldn't believe how good they looked. Sending people an introduction letter helped absolutely loads. Every new customer I give a short letter to them about the new system. You need to train your customers.
Oh yea, I lost one lady, but that was purely my own fault. Did the front door, and a little bit of water came through the letter box. Nothing much really. Thought I would just quickly do it, because she wasn't at home, I knew that she was gonna be trouble if she saw it, she came home lol. She was way to fussy really. First time didn't go right, didn't notice they frames were badly oxidised until it was too late, came back immediately the next day and re did them, they were perfect. I'm glad I don't have her anymore, all my custies are brilliant.
I just don't understand it, wfp isn't rocket science seriously. If you read plenty on this forum on how to do it, your gonna get close to a good or perfect clean. There are pitfalls, but you just need to know them. Most of all, you need to keep your eyes open, see what the water is doing.