It should not be confusing if a government denies charges of corruption, but does not attempt to rebut the accusation transparently. That's exactly what a corrupt government would do!
Corruption is not a problem, it's a choice. If corruption was a problem like bad water, underfunded hospitals, or not having safe harbors on the sea, then countries would welcome reports of corruption because the reports would be helpful in eliminating corruption.
Instead, a corrupt government official makes a choice every day that instead of providing citizens and other residents (and investors, import / export partners, etc) with a fair and predictable business environment --- where the cost of doing business is the same no matter who you are --- the corrupt government official grants privileges to people he or she likes and forces burdens upon people he or she doesn't like.
A worker who wants to reform a corrupt government agency will be met with resistance by his or her supervisor and peers. Within that agency, everybody benefits from the corruption---either by getting unlawful payments from the public or by satisfying the demands of those who do. Only an entity more powerful than the corrupt official can stop the official; this could be the organized public, a higher official, or a weight-pulling external organization (such as a trade body or aid provider) that can apply economic or foreign-relations pressure on the official.
After the 2010 earthquake in Haiti, news reports compared the earthquake's severity against the damage it caused; it was clear that similar buildings in similar earthquakes in other places don't crash down like that. ( https://www.theguardian.com/environment/damian-carrington-blog/2011/jan/12/earthquake-building-corruption ) Seismic standards are free information. So because the Hatian government knew (or should have known) the same things about safe construction that other countries knew, it seems likely that those buildings came down because of inspectors who did not hold constructors to actually follow the building codes, or who accepted their jobs without being actually qualified. In addition to stealing money, this is another form of corruption: but this is one that kills people all at once visibly and regrettably.
Another form of corruption, one that does not involve the government directly, is the incorrect approval of purchased goods for direct personal illicit gain. More than one engineer I know has reported to me that when they went to a large foreign steel-exporting country to evaluate the products they had ordered, the company had provided them with free access to prostitutes, either pretending to be the hostess of the business trip or the company's project manager. If my acquaintances had accepted these services, they would certainly not have had the capacity to evaluate the steel products to an objective standard---they would have felt quite obligated, or even pressured (under the threat of blackmail) to accept whatever had been provided. This, too, is corruption.