I think the most important part is "oil and chemical disposal isn't accounted for", as disposing of oil and chemicals would be the homeowner's responsibility an

I think the most important part is "oil and chemical disposal isn't accounted for", as disposing of oil and chemicals would be the homeowner's responsibility and would subject them to some very steep fines in many jurisdictions. (The mechanic would be acting as an agent for the homeowner; ergo, the mechanic is not responsible for chemical disposal.)