I have seen 38 cal many, many times, it was simply the approx caliber of 9mm into USA thinking.
So, take what the guys told you with a grain of salt, because a G date is obvious and much more rare than a 1938 (not hugely valuable rare, but much less of them made) {{not a slam, but lugers are a speciliaty and most folks don't know anything about them}}
No offense, but better pictures, full left, full right, cropped so you see more, front of frame, front and rear grip straps.
Value... you bought it from a shop, you should know the value?
What did you pay for it and we'll tell you what we think its worth