Bonuses are not intended to deceive investors. Giving out bonuses is a strategy adopted by every business not only cryptocurrency projects to boost sales. This is the main reason behind the bonuses projects offer during their token sales. And as the sales get to its close, the bonuses are lifted gradually hence it becomes an early bird catch tactics.
Well they really deceive people why? because giving bonuses in order to attract new investors even the whole project is a shit or pump and dump scam. this would lead their investor's losses since IEOs are pretty much pump and dump after the token sale since the tokens are already listed in exchanges unlike in ICOs although this will a good strategy for the company if they have a managed to convince people that have a good project that promises a good outcome. I also think that bonuses will result only on more pump and dump as investors sold their tokens after the IEO and the exchange opens them.
I think the big bonus cannot be said as an indication of a pump and dump project. In IEO there are sometimes new projects that provide bonuses so that investors are interested in investing. Big bonuses are common in marketing new projects and I think the pump and dump project depends on the developer team, whether they will produce a product or not.