>>15223051
Bars have lower premiums than coins and, when selling, you lose a greater percentage due to potential costs of assaying. Generally speaking, if you buy good quality coins (coins minted at world class mints that are very difficult to counterfeit due to the amount of pressure to produce clean strikes), there is no need to assay. Visual inspection is enough.
When it comes to gold, you can buy either coins or bars in assay packages. The bars in assay packages have lower premiums than coins and if you buy from a product made by reputable refiner, I don't think you'll run into the assaying problem when selling. I've personally bought bars from PAMP Suisse and Heraeus (kinebars). Credit Suisse is also a well-known brand whose bars you can buy.
As for silver, since it's so inexpensive relative to gold, I'm not aware of any large bars that come in assay packages. The smaller bars in assay packages aren't worth buying because the premium is so high. Personally, I think you're better off buying coins because if silver does skyrocket, you won't care too much about the premium you pay. The premium on American Silver Eagles is about $2.50/oz at APMEX (the premiums on silver Canadian Maple Leafs should be even lower) and if you think silver will hit $40+/ounce, you should be able to recover the premium when you sell since you ought to be able to sell at higher than the spot price at time of sale. If you insist on bars, you should buy bars that are from well-known producers and have tightly controlled weights/sizes. I actually own some 10 oz silver bars that APMEX produced so when I sell, I'll sell back to them.
As for literature, sorry, there's not too much to know. Buy product from trustworthy producers (US Mint, Canadian Mint, PAMP Suisse, Credit Suisse, Australian Mint, etc.) from trustworthy merchants. Know the difference between allocated and unallocated metals when not taking physical possession.