You will need to start a party from the Main Menu by pressing
. In order to unlock this you will need a second person;
I cannot confirm if this can be done with a splitscreen account or not yet.
According to Itzz Sh0wt1m3:
No splitscreen trade possible.
Once you have a person in your party, you need to highlight their Gamertag and press Invite To Trade. Trade any items you like and once the trade is complete you will get the achievement. Easiest one in the update to unlock provided you have someone you can do this with.
I should mention that you are required to trade and
receive an item. You can't do either/or as far as I'm aware.EDITS:
According to NoHeroes94, after extensive testing he speculates that item quality may be a factor for the achievement. Personally, I traded an Uncommon for an Uncommon and my partner and I both got the achievement, so you may want to anticipate that.
It popped first time for me, third time for him. I gave him a car (can't remember its value but it wasn't one of the above and it had a red background) and he gave me an uncommon item. That worked for me, not for him.
For the 2nd attempt, I gave him a premium item and he gave back the car. That didn't work for him either.
The 3rd, successful attempt, I gave him a rare for a random item and that unlocked for him.
To conclude, I think the item has to be of some rarity and not a premium etc. item.
This seems to imply that unbalanced trades (in his case, an Import for an Uncommon) might not work for everyone. The person trading the highest quality gets the achievement in this case. It also implies that trading something back will not work, so a boosting party couldn't pass an item around the group to get the achievement.
This is all speculation though, and as far as we know it could be a bug. Just to be safe, you might have to trade a few times to get the achievement, and if you do you should try trading different things each time.