(Maybe this can become a sticky. I'll try being as unbiased as I can as I run a lottery myself. I'm open to suggestions or things I could add/change. Dumb or not?)
Due to the psuedo-anonymous nature of Bitcoin and the ease at which games can be set up, Bitcoin gambling can be more at risk of quick scams.
Here are some things to consider when sending your hard earned BTC someone's way:
Is it new?
-The newer something is, the more discretion is needed. Scams usually come and go fast. With time, the reputable gambling sites will develop trust and players. Be suspicious of claims of big payouts when they have just begun.
Where does the random number come from?
-Random numbers can sometimes be faked. Some operators will use random numbers on their own computer legitimately. Others not. This is something to consider as the operator of the gambling site could be playing their own game. Also: getting a random number from somewhere else such as random.org doesn't really add anything unless it can be verified by others and they get the same numbers
How is the winner determined?
-Pyramid style games depend on others joining after you. Usually payments all go the same address and can be verified with blockexplorer.com. This only works however if everyone only sends payment using Bitcoin software on their own computer. Lottery style lotteries usually pick from a list of entries. How the winner is chosen is important. Can the list be checked somehow? Does the list also list the numbers for each ticket prior to the draw?
Is the operator a "flight risk"?
-some will open a Bitcoin gambling site with the hope of getting a big payout and then leave. Some pyramid scams operate such that they provide this interesting new idea then leave when people have paid. Others could be waiting to have a large sum in their hands then leave. It is also something to consider depending on how much money you "invest".
Does the game give you "deja vu"?
-often scams look a like. If it site/description looks like other scams it could be!
Bitcoin gambling can be fun but like all gambling it also has risks. Try to be aware of where those risks are. Pretty much any game can be played by the owner. By thinking about the operator playing you can see the areas where cheating can occur. Each area that can be cheated adds to the total risk. Choose what's comfortable to you.