A lot of roofs get replaced when they did not need to be. The deck and the structure decide the answer, not the surface.
Roof replacement is a large expense, and it is often quoted as though it were the only option. It is not. Between endless patch repairs at one extreme and a full tear-off at the other sits renovation, which is the right answer far more often than most property owners are told.
The way to tell the difference has almost nothing to do with how bad the roof looks from the ground.
The deck decides
If the decking is sound and dry and the structure underneath is intact, the roof is a renovation candidate. Failed underlayment, damaged flashing, poor ventilation, blocked drainage and a worn surface are all fixable without removing everything down to the joists.
If the decking is saturated, soft or delaminating, or if the structure has been compromised, renovation is not an option. Building a new surface over a failing substrate wastes the money entirely, and any contractor willing to do it is not doing you a favour.
This is why a real inspection matters. You cannot assess deck condition from a driveway, and photographs of what is actually up there should be part of any estimate you are asked to sign.
What renovation includes
Renovation means replacing the components that failed and correcting the conditions that caused them to fail. That usually covers underlayment, flashing, ventilation and drainage, along with any localized decking that has gone bad.
The important part is that the roof is restored as a system rather than patched piecemeal. Fixing a leak without fixing the ventilation problem that caused the deck to stay wet just means doing it again in two years.
Renovation also pairs extremely well with coating. Restore the failed components, then install a silicone or acrylic system over the top, and the roof gets both structural correction and a seamless protective membrane.
Getting an honest answer
Ask for photographs. Ask specifically about deck condition and moisture. Ask what happens to the ventilation and the drainage, not just the surface.
A written scope that separates necessary work from optional work tells you a great deal about who you are dealing with. We would rather lose a job than sell someone a replacement they did not need — the reputation is worth more than the invoice.