[quote=@Dusksong]
[@balthazar] Would trainer be able to "gift" each other items, and would they be able to "sell" Pokemon to each other for either TP or items? Because realistically it could happen, but it doesn't in-game.
[/quote]

Yes to gifting items or selling them at low rates. 

No to selling Pokemon. Trading Pokemon is okay though, obviously. They just have to be at the same tier.