How do I know that the website will be scammed?
ahahahah you make me smile

and it's not easy!
For example, if you know 100 people are a thief, who will scam you?
This is the same logic applied to your question
ALL hyip are scam, because such rate of gain are impossible, also a loan shark has a lowest rate... Why an hyip admin need your 5$

when he can just "double" the money?