While they usually are fainter, most S&W MIM hammers and triggers have case hardening colors. There are better clues to look for. MIM parts have shrinkage holes like the one visible in the underneath side of this 625's trigger. Frames with MIM hammers have the stud that blocks the cylinder's rearward movement while open forged as part of the frame. Older frames for forged hammers have a pressed in stud. Also, the pivot pin for hammer mounted firing pins is visible with the hammer forward.

To the O.P.;
With it established that this revolver has MIM internal parts you would be wiser waiting for a revolver without them. What did you say the widow's phone number and address are? I want to take her a box of cookies.