No need to mention because it's already obvious and even if we don't have any substantial evidence to prove our speculations, it is already safe to assume that there are negotiations happening behind the curtain to increase their chances to host the next World Cup.
Money is not really a big deal here if they bribe someone within the organization because the sky rocketing profits in return will not be comparable to what they bribed.
Yes, it's probably safe to say they moved behind the scenes to negotiate. And from the word negotiation, anything can be done to make the negotiation go smoothly. Negotiations will always be there, and one of the clean and healthy negotiations when they give a presentation of what the country proposing to host can do, they can sell that to make FIFA believe and entrust it to that country. But the question is when the negotiations are done behind the scenes and no one knows about the process. It is natural that in the end it raises suspicion.v