If possible a mechanic will endeavour to fix the issue identified during the inspection time booked for. In many cases, though, new parts will be necessary to fix the problem. Should this be the case, then the mechanic will quote you for the labour and parts needed to fix the problem.
When you agree with the quote then the mechanic will try and source the parts and fix the problem at a later time. In some cases, though, due to non-availability of the parts or a shortage of time needed for the repair, it might mean that the mechanic will have to return on another day.