It's quite obvious. There are a lot of warning bells that should hopefully get any scam sites out of your way:
1. Admin cannot speak good English
2. Admin has a history of scamming, or spamming
3. Domain registration is only for a year or less, when they claim to be here for the long term
4. Any "HYIPs", "Doublers"
5. Anything that is too good to be true.
These might be signs, but all of them can easily be avoided. The hyip admins are becoming smarter and smarter and are always coming up with a new idea to scam people.
1. Everyone are capable of learning English. Most people can even master it.
2. The name of the admin can be easily changed. I think that hyip admins are mostly the same person but has different identity and whereabouts.
3. If they have enough money, they might as well have purchased a long term domain. Or maybe come up with some "we'll extend it later" announcement.
4. Other people don't understand that and most HYIP sites don't put these in their website. They just say that they offer this lifetime plan, etc.
5. HYIP sites have been offering 3 months ROI which is good enough to be true to most people. And even if some doublers only have 100 hours to wait for your money to get doubled, they always have a reason or an explanation on how is it happening.
I agree the HYIP scammers are not dumb they are getting smarter every day, other things I have seen HYIP scammers do is they have scripts that allow them to create fake info of people, names directions and earnings, they buy fake testimonials, sometimes they even have video testimonials.