the worst purchase I ever made was when I first strted keeping fish a little over a year ago when I got my 55g tank. I didn't know anything about fish. Instead of surfing the web for information, I figured that I could get the best information at petco. Wrong!!! I went there for gravel and was asking the guy for fish information and let the guy talk me into buying 14 gouramis for this tank, the same day that I bought the tank. They survived the cycle, but by this time, I had figured out that they were some really mean fish, so I ended up taking 9 of them back. The other 3 died in fish fights.
Worst restaurant; Hardes. we went there for lunch one day and ended up sick for 3 days. place closed down about 3 months later.
I got some bad gravel in walmart once. Everytime I put fish in my niece's tank, they mysteriously ended up dead in a matter of hours. I had a little over 4" of gravel in my 55g and replaced her gravel with some of mine. The coating on her gravel had some kind of toxin in it that always colored her water.