"What I do when someone begs me is I trade them then put all the crowns/CE I have, unbound items, and any 5* SL materials or regular materials I happen to have. After they start drooling at the items, I just go get something to drink and come back then once they close the trade I say I was lagging and I'll give them the items now"
Heh... this sounds hilarious to do, but I fear my little brother would come click trade while I was gone to purposefully &^%# me off....
If someone tries to beg me, I often ask for mats like monster bones-bushy tails, and buy them from 10-20 cr each. If he/she hasnt got mats, then close the window.