My reference was to finding myself agreeing with Apple ... again!
Is there no end to that?

Okay, Fredo might have been so unintelligent that he was not able to see the potential consequences of his actions. Didn't he tell Mike that he didn't know it was going to be a hit? Such lack of intelligence implies that Fredo did not have to be promised much by Ola. Keep in mind that Fredo was already running some portion of the Corleones' business. We can't be sure, but he probably had a substantial income, command of troops, and the respect that comes just from being a Corleone. What else could Ola offer him? Plus, if he truly believed that it was not going to be a hit (only a wounding?), how in the world was Ola going to deliver the promised "something" without Mike finding out ("Hey Mike, Ola's giving me a casino in Havana because he likes me"). Also, what was Fredo's reward from Ola since he apparently did do something (the drapes?)for Ola/Roth, didn't he? Was he stupid enough, as someone else has suggested, to think that he could be the Don? Yes.