Hi again Doris: Again, I apologize, but this is not my area of expertise, so I can't offer you too much detail, but I can offer a couple of broad points.
I would not have an inspection accomplished by someone who is in the business of selling or installing flues....there's a conflict of interest there. And how do you see pinholes by putting a flashlite down a flue? You see pinholes by putting a flashlite outside the flue (backlite) and then look down the flue or chimney. Besides, how are pinholes going to create a hazard? The small amount of smoke that may get out the pinholes (if they are there at all) will simply rise up alongside the metal flue and out the normal chimney, wouldn't they? (providing there is not a tightly sealed cap on the chimney top) The only reason to install a metal liner is becuase the chimney brick are in poor condition or lined with tar and creosote, thus a fire hazard.
IMO, the most important factor is the lack of creosote on the lining of the flue. If there is none, if small amounts of leaking smoke has an excape at the top of the chimney, and if the metal of the flue is intact (not rusting through) then I can't think of a reason to replace it.....can you? :-)