Can't make any Adjustments on my trailer brakes

OK he may not be an idiot but since it is apparent he did not test his work before he gave it back to you he certainally is incompentent. And not worth trusting with any other work. As a mechanic i learned many many years ago to test at least once my work before I returned the product to the customer. I never wanted a comeback for any reason except because he was happy and wanted more work done.