I would personally use seduction for bribery, but if I were using both, that's the best description of the difference I ever heard.
Assuming Seduction, Duping an Intimidation were in play:
Seduction implies a positive rienforcer (a reward), Intimidation implies a negative rienforcer (a punishment) and Duping merely implies you are attempting to lie to or trick the target.
In the context of an interrogation:
Seduction would imply the use of "Good cop" strategy ala "tell me and we'll let you go". You are trying to draw out the target with the promise of a reward.
Intimidation would imply the use of "Bad cop" strategy ala "Confess or we're going to cut your fingers off", draw out the target with the threat of punishment.
Duping could be a part of either of the above, in the sense that you could never intend to let them go or cut their fingers off. (if you actually intend to follow through, you don't need to be a good lier, as you are actually telling the truth) or it could be used on its own ala "Your partner already confessed, we just need to settle a few details, he says you stabbed the elf, is that true?" when in fact the partner is refusing to talk and you're lying.
Diplomacy, at least the way I use it, when I use it, involves more complicated matters involving balancing multiple factors against each other. Like if both criminals, representatives of their families, and the dead elf's brother are all in the room:
"If you confess we'll put you in our jail for 25 years, your partner will be turned over to the elves for punishment. Your family will pay the elves 10 GP indemnity, your partner's family will pay the elves 100 GP indemnity. The Elves will be satiisfied with the payment and punishment of the actual killer and make no further reprisals. Is this acceptable to everyone?"
If a PC had Diplomacy but not seduction, bribery or intimidation (when those skills are in play), I might let them use it at a higher difficulty level to do tasks better suited to the other skill.
Likely that would be the same answer for any of these skills cross used. (i.e. intimidating someone into taking a bribe ala "Either I pay you or I break your leg") within limits of course, like intimidation is no good for a "soft" attempt at using the seduction skill.