I worked nearly eight months in a lfs finishing just over a year ago when I fractured the disk in my back, causing it to compress my spinal column (I hasten to add this was not caused by the job).
Prior to my starting I had over 30 years fishkeeping experience, in depth knowledge on many species and what I thought was a good general coverage of most of the other aquatic areas. Nothing could have prepared me for the massive range of questions I was asked about absolutely everything in the shop and more. In the way of dry goods I learnt to repair filters, replace all types of light bulbs, where starters were located, set up every type of filter available for sale, know which filters came with media included and what it was - a mere drop in the ocean. There is so much out there that one has to ask the others in the shop and not worry about doing so.
I also learnt that when someone has a problem it is rare that you are given the whole story the first time you ask. Sometimes you need to ask the same questions many times, just phrase them differently and eventually the whole story will come out.
I can't recommend any good sites for it but these forums might be a good starting point. They need to be relevant to NZ conditions e.g. as here in NZ you can get very few strong over the counter medications. There are also NZ facebook pages. But as with everything you read, you need to sift through the answers.