It's preferable to trade with someone who has their own Pokemon for a variety of reasons:
- You're trading for something they got themselves, not something that has been spread around the Pokemon community like a bad case of STDs.
- If something is wrong with that Pokemon (ie, it's hacked) you know who to blame for it, and appropriate measures can be taken.
- It's nice knowing that someone else put the time into getting something, and that you're trading your own hard work in return for theirs, instead of someone trading something that they had no role in obtaining.
If you have any further questions about this, please PM me, so as to stay on topic in this thread (relatively, anyway).