Just in case you didn't know, the coins that are used for achievement for fishing in the Dalaran fountain are not bound or anything and can be traded or sold on AH. So if you can't find your coins, and your friend got 'em, trade between each other and get that achievement. Also glance at the AH to see if someone is selling those coins... you don't have to think the worthless and throw them away, I sold a few at 5g each (I could have sold for more) on my server. Easy gold and once you catch a coin, the achievement is counted and you don't need to keep it anymore, you can AH it easily.
Oh and.... something that made me huge amounts of gold!! buy those vendored non-combat pets for 40s each and sell them for 5g each on AH.
Hope these tips come in handy for someone or the other. Will you believe it if I told you I made over 1k+ gold just buying moths from Six a vendor in Exodar for 40s each and selling them for a small price of 5g each on AH? Always count on the laziness of players to go to Exodar! lol
Happy leveling all.