I agree with Dylandrewsdad. When I first started out, I knew absolutely nothing. My first "big" tank was an 18gal tall Eclipse 1 system that housed my first sorority (nine females). I was advised to put a "small" pleco in it to help with the algae. That "small" 2" pleco shot to 6" in the three weeks I had him and eventually fouled my filter. So, I took him back and got a few otos. Those actually survived for over a year (through me not knowing about cycling or anything like that) until my 55gal crashed earlier this year. Then, I upgraded from the 18gal to my 46gal bowfront. Again, I knew nothing and just plopped the fish in the tank without cycling it or anything. Amazingly, I didn't lose any fish from this. I also didn't know about water changes or appropriate stocking. I joined a forum (this one, I believe, actually!) and found out about cycling, so I took some water to be tested at my LFS (had been warned against Petco/Petsmart) because I couldn't afford a test kit. I was told that my pH was too high and my ammonia was off the charts because of the pH being so high. So, I was sold some pH fixer crap and told how to use it (a friend ended up paying for it because I was completely broke). The pH crap made things worse, as it sent my tank into a mini-cycle and I had a MASSIVE bacterial bloom. So, I got pissed and started doing my own research and got myself a master test kit. Imagine how much easier life is now that I don't have to rely on the LFSs or Petco/Petsmart to help with my water parameters or my stocking.
I don't blame the LFS person for what happened with my 46gal, though. I went back and told her what happened and she seemed genuinely perplexed. She had actually showed me the tubes compared to the charts, so I could see for myself that my pH was really high (8.2, which is what it is out of the tap) and that my ammonia was high as well. Most times, LFS people just aren't well-educated enough in aquaria to help out. My LFSs and Petco/Petsmart know me so well now that when I go in to purchase a fish, they don't grill me about my setup and tankmates anymore like they do other customers, they simply ask which tank the fish is going in and then comment on how they think it'll look in that tank (not if it's compatible or not).