complications
"I think it would depend on the intent of the seduction. If the character was merely seducing out of a desire for anything other than the affection of the mark, then it would be a Bluff skill. If, however, if the character really wanted to attract a potential mate through seduction, then it would be a diplomacy check.
Working with the rules as they stand, I think it works well (enough),"
That should be the basics. Bluff assumes you have something to hide, so if your intentions are hump and dump, or persuade the guard to leave his post, or... a bluff check is in order. And if your intentions are "honorable" [which would include offering gold..], it's a diplomacy check.
But there are a lot of complications. When she asks if the dress makes her look fat, a bluff check is definitely in order [or a con check on your attempt to run at top speed.] And most seductions will involve more than one roll, and most of them will be diplomacy rolls whatever your intentions.
Some cases will involve both rolls. You fail the bluff, she knows you just want her body. But you get a really great diplomacy roll and she decides you are a great guy worth giving it to.