Whitepaper
I check if whitepaper is plagiarized or not. Scammers simply copy from various whitepaper and use this in their whitepaper. You can do it with various free resource of plagiarism
On the serious note, scammers can also hire someone who's very well in writing whitepapers and has various experiences doing it. As you can see, just lurk on the services and marketplaces, you will see someone offering this kind of service.
Exchanges
If IEO is launched on Binance, Kucoin, Gate, Houbi, Okex. I always appreciate it. They are promising
So, if the IEO isn't on these exchanges you wouldn't care to look at it?