It has always puzzeled me that the rings given to Men were way more pliant than thoses given to Dwarves or the Elvish rings.
Why were the nine more suseptable than the seven? Sauron had them both, but he appears to have corrupted Men way more, or we would have (three or four, I can't rememeber) short squat Wraits running around Middle Earth.
at the short squat.
Din, I haven't the english version of the Sil, but I try to translate the passage that came to my mind here - look into the chapter about the forging of the rings.
There it is said that the men were more likely to fall under his reign as they were proud. And we all know that pride cometh before the fall. As far as I understood it weren't only kings, but also magicians and mighty warriors. The people of Dunharg, the black Numerórans, the Eastlings and the southerners. People from Umbar, Harad and Rhûn are very likely candidates.
The rings were forged around 1500 second age
1800 onwards Sauron extended his power eastwards
2251 Nazgûls appear
There might have been some folk in Middle-Earth that wasn't very fond of the realm of Númenor and maybe even jealous. Aren't there better people to corrupt?
The Sil further says that the dwarves were obstinate and hard to reign - talk about stubborn dwarves....
. The thoughts in their hearts were hard to find out and could not be turned into shadows.
At least the rings planted the desire for gold and more gold into their hearts. This desire lead to enough trouble and quarrel and war to please Sauron.
When it's said that Sauron got three of these rings back, I suppose it happened when the dwarves lost against Saurons troops. Or like the one Gloin mentiones. As far as I can remember he said that the dwarves went to Moria to search for one of the rings. Gandalf replied that this ring was taken with torment from Thráin in the dungeons of Dol Guldor.