General Forum

It does seem like a question of one's particular interpretation of etiquette. I leave my feedback after I mark something as received, but leave the trade open because I feel that marking it 'completed' might give the impression that I am 'done with it'. It's akin to a waiter dropping off one's meal, leaving the check on the table and never returning to see if anything is okay. By declaring something as complete before it's actually completed, it might telegraph to the other person that one is not interested in further communication (even if that's not necessarily the case). Since I am in no hurry to shovel off transactions into the Completed tab, I don't mind waiting until I see the other person has received things first before marking it complete. 

Here's a good reason to wait. You receive your cards and everything is correct, The other person receives there cards 1-3 days later and finds one of the cards you sent is wrong, Your responsibilities are not "complete". 

Doesn't happen often but I've done it at least once.