I am offering a lvl.100 gardevoir for an arceus any level and no one is trading, why is that?
Probably because very few people have Arceus. You just have to be patient. Maybe try offering a more rare pokemon like Milotic or a legendary.
(Side question: how are you able to request Arceus on the GTS, did you "see" it somewhere?)
Maybe its because its a great pokemon and no one wants to trade it. If you really want one,just be patient.
not alot of people have arceus and if they did they would wanna keep it