Ha ha, of course, doctors can't be counted as sales. The high registration fee for experts is because the threshold is set to take up time for some problems that can be solved without experts. In addition, it embodies a different academic authority, and it is also an incentive for doctors to motivate themselves. (The incentive mechanism is a reward, and the reward is graded. The grade, including the registration fee, is determined according to the degree of public recognition. ) So it's not a business.