It isn't that people don't trust you. I am sure if you were a well-respected member on another site and someone new with zero feedback was going to sell or trade you a card and you had a good amount of feedback you would ask that the person send first. (am I wrong?)
We have a Verified Trader Program to ensure safe trading practices on our site. Rest assured if you are dealing with a Verified Trader there is nothing to worry about.
Again, it is nothing against you personally. Many new members are required to send first when making deals on this site. It is to prevent some random person strolling in off the web saying they have a sweet card (with no scan) and then just disappearing without a trace once they have received payment.
Glad you were able to work a deal. Please feel free to fill out the Verified Trader Application if you have not already done so.