How do I resist buying new, fancy fish, that I've never seen or heard about? Easy...
I think to myself, do I really know how to house it, feed it, treat it and all that? if I realise that I don't even know what is the best temp. for them or don't even know what PH it requires, I simply don't buy it, and maybe get a plant or something instead.
I mean, I'd feel less guilty and sad if a plant died, rather than the latest fish I bought just because I thought it looked cool and it died because I couldn't house it properly or I didn't know ehough about it. Plants are much less, requiring(?) shall we say.
So that's my advice to you. Ask yourself if you can really house the fish or whatever you're buying. If you can't, go buy some fancy fish flakes or treat your fish to some live bloodworms. Or if you're like me, go buy a plant or decoration if you really want something new to add to your tank.