If you can't supply the above, we might as well imagine. What was your win chance and did you have any previous gambling luck to get you that 700 mBtc? If so, i'll just say that you should've cashed out.
Why are you so bothered about seeing the screen shot ? I mean let him fake whatever he wants to ,what if he shows you a screen shot ,are you going to refund his money ? If that's not the case then I don't see any reason why would someone even create this thread.If he would have won a good amount of bitcoins from a dice site,its legit to ask for proofs but in the losing case ,I don't see any relevance here.Why would someone be so glad about losing money anyway?
@OP : Care giving more details like which game ,what website ?
I can understand that he lost such a huge amount but many have lost their bitcoins while gambling and with the recent bingo competitions, it has made more users addicted to gambling.