I'm not sure if it really counts as an Exploit but I found out yesterday by doing the fishing daily quest Moat Monster! in Undercity that theres a bug that lets you finish it pretty quick. I had a download in the background running and a high latency. When I threw down a frog to that tentacle I clicked it a few times before the first frog fell down and suddenly I was on 2/10. On my second attempt I repeated that with some faster clicking and was at 7/10. I guess if you use the same technique/macro as for the tabard vendor you could just do a 10/10 with one shot.
It's not a big deal though - just a little time saver.
*edit: it was the fishing daily, not cooking.