Whenever I use the WT, I give away whatever extra IV breed Pokemon I got left. Just the other day I gave away a nearly perfect 31 IV breed and EV'd trained PKMN. I'm sure that individual was really happy with. I always use it without any expectations. I'll admit that I've had my fair share of unwanted pokemon but I've also gotten some pretty cool ones too.
I think it's a pretty cool feature.
peopel that just send bcak the trash they get on wonder trade are part of the prblem since they just send away tehm agin for another unliucky player to get
3 Pokémon I can use out of 5 boxes of Wonder Trade severely crushed my spirit - but it was worth it after all, because I got nearly 50 Rare Candies in return.