Friends, or friends who do express delivery, tell me, if the same product is sent to the same place, will the freight charge be different between 30g and 40g or 80g?

Express delivery is charged by kilogram, and less than one kilogram is charged by kilogram. Compared with 40g or 80g, the 30g you mentioned does not exceed one kilogram, and there is no difference in price. The freight standard depends on what kind of express delivery you use (if you send it by post or with the wind, the price will be slightly higher than other express delivery) to your destination (if you send it to remote places, such as Tibet and Xinjiang, the charge will be higher).