Even at 29, I would be happy to get a player of his pedigree at 25m. That's how inflated the market is, especially in January. It's a good fee for Marseille considering West Ham only wanted to let him go at 40m initially.
Anyway, think Payet left West Ham for personal reasons. Accepted a wage cut to play for a team likely to not have any european football next season, gave all of his January wages back to West Ham.
I'm interested to see how Gabbiadini will fare for Southampton, interesting signing.