The local security and intelligence agencies are often harassing the shopkeepers in an area, telling them to extort money or create other problems for some customers.
These targetted customers are aware of the fact that they are discriminated against, and will often refuse to pay the higher price which is being demanded from them., as they are already broke.
So these customers will often prefer to visit trade fairs and exhibitions , because the local intelligence and security agencies will not target the exhibitors and they will get a better price. The exhibition is for 3 to 5 days only , so the local security agencies do not take the effort, as it is not worth spending so much time, taking the risk,