I personally use three LFS's. I have to travel some considerable distance to use two of them but I do so because they really know about fish and will answer questions (for free) when I have problems. Another LFS, my nearest, is very good in terms of fish care (for instance, they checked that my tank was cycled and that I had appropriate tankmates before allowing me to buy a betta), but tend to have only the most popular species and we have differences of opinion over some issues (they sell danios for cycling new tanks).
In these good shops I find that all the employees either know what they're talking about, or will always go and find out if they're not sure. And don't be put off by their youth - some young people know more than some of the older people sometime! OTOH, I sometimes wonder if these assistants are working for cash, or fish
I think once of the tasks of a newbie is to find a reliable LFS. No one's infallible, but if they take care and know what they're talking about 99% of the time, that should be OK. The advantage is you know the stock is healthy and you are unlikely to be sold totally incompatible species.
If an LFS or pet shop isn't like that, you could buy fish that carry all sorts of diseases that you'd introduce to your tank, you could be supporting a business that is inhumane towards fish (mentioning no names!) and you could even be supporting a business that is not so careful about importing rare species illegally!