Some people banding together to rob the shopkeeper is something that has happened many times in the past. Many people try to rob him because they think he is weak and can be bullied.
The cultivation technique that he uses is so profound that it has many layers of stealth. On the first layer, he appears to be an ordinary person. Those who can't pierce the first layer of the illusion will believe that he is just an ordinary mortal.
An ordinary mortal selling cultivation techniques for the third mortal coil of cultivation is a prime target for robbing.
Even the people that can see past the first layer of the illusion and see him as a cultivator as of the first mortal coil or second mortal coil still feel that he is a suitable target for robbing.
