Right when retainer ventures came out (2.2?) and they were broken and bringing back things they weren't supposed to bring back, someone put the Manor Harp on the MB for 25k. I bought it and re-sold it for 1.5mil.

Have found various mistakes by people obviously putting the wrong price on things, but none as profitable as this one.

I haven't needed to try and make money since that patch anyway. I flooded Goblin server with Glazenuts. Probably sold about 60-70 of them for 500k each.