Plenty of people are still making 5-10x ROI on ball pythons within two seasons. The market may be over saturated with the species but it is not over saturated with certain mutations. I'm not even sure that it's over saturated at all. Millions of people are out there that would buy BPs if they knew there were mutations or that they were possible to own at all.
No one can tell you what to invest in to make good ROIs 100%. You can look at the trends but in the end there is still risk involved which is why you make a profit when things go good. If people could tell you where to put your money and reliably make it pay off, they'd be multi-billionaires.