i have never had a problem with credit trades and i have done many, but i have also only done credit trades with fellow disers. i guess my only word of advice would be if it is someone you have not done credit trades with before , then get your item or items first. if they won't agree to it then just tell them no ty and end it there. patience on getting what you want will play a big factor as well. just remember there is always another player trading the item you want, so just shop around until you find someone willing to do it your way next.
sorry to hear about your loss and good luck to you on future trades.