Re: the Model 19-3...
The Model 19-3 is one of the more common M19 variants, with a production run that spans a decade.
If the gun has the more common 4" or 6" barrel, $675 is towards the top of the value range. At this price point, IMHO the gun should be in legit 95%+ condition, with original numbers-matching stocks (i.e. grips); the numeric portion of the serial number should be stamped under the RH panel. A factory box, factory wood presentation case, nickel finish, and/or 1/2"-wide Target hammer and trigger and oversize Target stocks- known as "3T's" in conjunction- would help justify the price.
If the gun has the less common 2-1/2" barrel, it is worth ~$100 more in equivalent condition; I would not necessarily expect the extra "goodies" for this price but I would expect >90% condition.
However, I basically agree with sarge83- if it's not something like, say, a legit LNIB nickel "3T" gun in a factory presentation case, I would try for $600 or less. The average holster-worn 4" blue M19-3 with the standard hammer, trigger, and Magna stocks, and no box, is IMHO a ~$500-$550 gun, period.
"Smokey, this is not 'Nam. This is bowling. There are rules... MARK IT ZERO!!" - Walter Sobchak