Sentence Correction

This is from Manhattan GMAT SC book

In GMC advanced chapter

Although most consumers are suspicious of such offers, colin wants to purchase the two-for-one vacation package.

Consumers suspect such offers is unidiomatic.So I cannot modify the first part of the above sentence.

But the sentence

Many directors have a suspicion of there being an attempt by managers to conceal the extent of losses at the company.

Can be modified to

Many directors suspect that managers are trying to conceal the extent of losses at the company.

Could any one please explain when should I consider changing "suspicion of "or "suspicious of "to "suspect" ?

Can someone please clarify the aforementioned doubt; even I am looking for a clarity.

Thanks.