Do not only trust with on gambling site, there are a lot of legitimate gambling sites where you can diversify your investment and it's a must when you are an investor as that will help you minimize your loses. A site could offer you a great return but always consider the negative side also, it's best to use our head and be smart all the time.
If you talking about investing in a bitcoin casino sites then I can easily tell you that there arent many trusted sites that you could invest in. Besides that the wagered amount daily is actually one of the parameter for us to choose wether or not it is worth to put our money on the sites, if it has low wagered daily then it is not worth it