One of the easiest and time-tested methods to buy gold bullion is to buy it directly from a reputable local gold bullion dealer who's been in business for a pretty long time. Why I prefer to get it from a dealer the good old way is coz you can see and feel the gold bullion - also you can actually feel the weight of the coins before you buy.
It's most likely the best approach to buy coins that are actually issued by a Bank or a Government agency than to buy the usual 1 oz or 10 oz bullion in the open market.
Usually you will find in most cases that the bullion that you plan to purchase is assayed or usually tested (acid) to check that it is real. But if you buy gold bullion encapsulated by a the very reputed issuing company it usually comes in a tamper proof case so there's really no question of purity or safety. Well, if you happen to invest in gold, you must clearly understand that it is a very long-term proposition since once you have it, it doesn't do much. Much in the sense, gold bullion doesn't pay interest or dividends but I would think that it is nice to take out and look at from time to time and feel it in hand often.
Also, be prepared that in short term you may infact likely lose money due to the market but eventually inflation increases it's value over a long period. The recommended allocation that most wealth manager's suggest is not more than 5% of your total portfolio's value should be in precious metals. Also, here's a very important tip when at the dealer's outlet, make sure that you are not charged more than around 10% over the current spot value of the metal. Remember to check online to see the daily spot value's and keep yourself updated of the up's and downs.
Finally, remember to keep the gold bullion, encased in it's original protective plastic Air-Tight packet since condition (in the distant future) may be important when selling. Hope you found this stuff interesting and useful.