Almost every phone shop repairs by replacing: a screen, a battery, a port, a whole board. That covers nine faults in ten and there is nothing wrong with it.
This workshop exists for the tenth. When the fault is one component on a board the size of a bank card, the only repair is to lift that component off without taking its pads with it and put a new one on, and that is done at forty times magnification with hot air, flux and a hand that has done it a few thousand times.
What it means for you is that a phone another shop called finished sometimes is not. What it also means is that the work is slow, it is charged by the hour of looking rather than by the part, and a fair number of boards are genuinely finished. We will tell you which yours is before you spend anything beyond the assessment.