Airlines have what is called RII or slang R double I. Required Inspection Item. Essentially someone has to be happy with your work enough to co sign the job. When I do something, I do it as a mechanic. I stop in my head and become the inspector. I was a QA/QC inspector once upon a time so I was stuck signing my name to other peoples jobs. When I can, I try to get someone to go after me, even if not official. I also will not preflight someone else's airplane. I am a one man shop for the most part, and I am not the neat one. One minute I am doing a Annual and the next I have a flight line problem. I clean up for different phases of jobs, but most of what is used stays with the project till done. That is only possible with a one man shop. Add another, especially one you are having to go behind and that does not work. I do go to completion points like all engine mounts to completion, or one flight control to complete install. For the most part the divisions have to be in my head cant afford a 300'x200' hangar.