You are correct crudos - Even if you had a letter (provenance) written by your grand Dad stating where he got it and how he got it, the value would be higher.
Now with that said, a new Standard Browning Hi Power is around $600- with an extra mag. You add on the target sights they go north of there to $990- which I have seen at Cabela's in Hamburg, PA.
1) 1000M, you know and I know your grand dad's hand gun is worth more then $750- to the right
person (WW II Buff)
2) Even though the appraiser has his head up his butt, I would hold onto and Cherish that hand
gun. Maybe write your own provenance letter so that your heir (s) may get a higher appraisal in
the future (Can I be one of your heir's?)
Good luck and shoot it once in awhile.