How to choose a good supplier for roll forming machine?

Open Googel,when you seach it ,you will find too many advertisment rush into your eys.Which one is  good supplier,the machine from which company is the quality one? Then Let me tell you tips.

1.Neither buy the expensive one nor the cheap one,just choose the middle one.

2.Check the aftersale-service ,Longer Gurantee is always good for you.

3.Talk with the sales (by phone better) for long time ,to understand their products,their company and their service.