When you encounter this kind of problem, don't look at the process, just look at the result. Neighbors certainly don't make money or lose money, and customers take the boss's loss.

For example, Master Wang sells shoes. A pair of shoes is bought in 20 yuan and sold in 30 yuan. 20% discount on National Day. A customer came to buy shoes and gave a dollar from 50 yuan. Master Wang had no change, so he asked his neighbor for 50 yuan's change. Afterwards, the neighbor discovered that the money was fake, and Master Wang lost his neighbor 50 yuan. How much did Master Wang lose?

The customer took 1 pair of shoes (the purchase price was 20)+26 yuan (26 for 7.4% off), so Master Wang lost 46 yuan.