Finnick Odair was based on Ozzy Lusth (and a little bit of Parvati)
Basing this solely off of Cook Islands/season 13, as Micronesia and all of Ozzy's subsequent seasons would have happened too late (Micronesia was 2008 so not technically too late but I haven't re-watched that season yet).
For name comparison, Oscar (Ozzy's full name) means "God's spear" in old English, which is very similar to a trident in a sense, so I think if Suzanne researched Ozzy's name or anything it could have inspired Finnick's signature weapon. Lusth means lust, which is a bit of a stretch when comparing to Finnick but not entirely so.
Ozzy was a menace in the water. He was the ultimate provider, with his spear fishing. Not to mention he was such a good swimmer he would lap everyone in the challenges and just dominate. Finnick was a very dominating force in his games, so I feel like Survivor's dolphin boy could have easily inspired the Sex God of Panem.
Bonus, but I think Parvati also inspired Finnick's Capitol personality. Her flirtatious nature was indeed a second nature to her, but she mentions all the time in Cook Islands and later seasons that it's strategy for her. I think Parvati and Ozzy's antics in the hot tub definitely could have inspired Suzanne when she was conjuring up Finnick. Parvati could have also easily been Inspo for Gloss and/or Cashmere. Time will tell. I really want one of their books but I don't think we'll get them. I think (and hope) Annie's Games will be next if we ever get another book.
Circling back, even though I haven't rewatched Micronesia lately, I have seen it before, and it was a Fans v. Favorites season, and Ozzy was a favorite, in the same way Finnick was a Capitol darling. Ozzy also had a showmance with Amanda that season, and it's a bit of a stretch but that showmance could have inspired/reinforced all the Capitol showmances Finnick was forced to put on.
So to recap, I think Ozzy's fishing/water/challenge prowess, and his and Parvati's flirtatious personality are what the character Finnick Odair was based on.
The one caveat is that Ozzy is never described as drop dead gorgeous like Finnick is, but Finnick would NEED to be beautful for his plot, and Ozzy was HOTTT in his early seasons 🔥🔥🔥