1. Give people a time-out if they forfeit a wild fight to help with the people camping the rarer pets and bailing when the stats don't match up. It sucks to go into a fight with a little semi-rare humanoid knowing their are 3 more up on the minimap going in, and coming out a little over a minute or so later and seeing all of them gone and not a person in sight. Could work it just like the time-out on dungeon ques.
2. Allow trading of wild pets but make everything that is caught be level 1 when captured. I get the idea of not allowing wild pets to be traded because people can sell a level 23 snake they just caught to someone and they could then go on and get all the achievements. It would be easy. But you allow it the hard way by allowing people to sell pets they have leveled that can be traded (vendor, drop, seasonal). So what you are saying is, it's OK to buy a pet and get these achievements but we're going to make those 25 levels have real value... so do it with the wild pets too! Make them all level 1 when caught.
(Or you could give us the option to say "tame this creature" which would make it level 1 and tradeable, otherwise it would stay as a captured wild pet and be untradeable and maintain it's caught level... just a thought).
All this comes down to two issues, they don't have to be handled this way but I'm sure the themes can be ascertained. Addressing these two topics could improve the quality of this whole experience immensely. This first being FAR more important to look at than the second.