I did some calculating. Now I know all miners are different and we don't know the "age" of his equipment. But I used 4 different Bitcoin calculators to estimate what I should get for the 763 ghs I have which were pretty close to the same.
Now, these are just examples and I realize that in no way without knowing his equipment, etc. and what the calculators use for "equipment" we may not be comparing apples to apples, but here goes.
I got 0.05370662 BTC for the 763 ghs. So I am being shorted about .014 BTC which to me is not a little amount. Taking the lowest of the calculations, that means we are getting about 80% of what we should be getting (.05370662/.06713805 = 79.99%)
Following are the results for the four calculators:
40,007,470,271 is what all four say the difficulty is for this week.
1. https://bitcoinwisdom.com/bitcoin/difficulty .06714
2. http://www.bitcoinx.com/profit
(had to put in the proper difficulty) Calculation says .0096 bitcoins a day which is .0672 bitcoins a week.
3. https://alloscomp.com/bitcoin/calculator 0.06713805 BTC They also project with lower difficulty next week it will be 0.07091265 BTC
4.
http://coinbrief.net/c/btc/mining/ 0.06713908
I do not know if this makes him a scammer or not or if his equipment is just old.