Just understand their expectations of what you need to achieve. The reality is that people can lose weight very quickly, but often the tactics used are exaggerated and unrealistic for most people.
This is why so many people do it, who often go back to their old "normal" ways, with a little exercise and a healthy diet, "they eventually gain all the weight back."
All the hassle of starting and ending with mixed results is ultimately very scary and frustrating. Many just give up