I think Primedice is the best dice game. I lost 20-21 times in a row. But I don't have a proof to say it is a scam. This is natural and it's possible.
It is indeed very normal for a gambler to lose 20-27 streaks in dice game then he loses or 17 and thinks that it is already a scam site. On that terms i myself can consider that OP is probably just new in gambling industry or in the dice game it self