It’s an issue that Marxist economists debate about. We have ways of calculating the costs for machine depreciation (so we can factor maintenance into surplus value), but it can get really difficult, or is sometime impossible, to calculate things like the value that a transport worker adds.
Meanwhile for commodity / direct producers, surplus value is an easy calculation: worker value added - wage paid.
There’s also the issue that transportation and point of sale workers are in different economic sectors, in many different countries, which has implications for their place in the class struggle. John Smith’s I imperialism in the 21st century gets into some of these.

























People are not inherently evil. Your pessimism was indoctrinated into you, and you can be undoctrinated from that wrong view.