Need to know who you are dealing with and who they are dealing with as well. Tungsten salted bars have turned up as being passed off as gold.

Images below courtesy of this article.

http://www.businessinsider.com/tungsten-filled-gold-bars-found-in-new-york-2012-9

Also be aware Gold is sold in Troy weight and don't get conned in by those hawking grams of gold such as found in jewelry and "clad" or "layered" coins.

Sovereign coins while costing more in premium tend to be safer from salting although I have read of  few cases with them as well.

Canadian maples are 24 karat gold, US Eagles are 22 karat gold, Krugerrand's are 22 karat also.

All contain 1 troy oz of actual gold. The Eagle has silver/ copper alloys, the Krugerrand has copper alloys to make them tougher and harder for actual handling. (This gives the Krugerrand's their more distinctive reddish/orange hue)

Maples have higher purity but are softer and more prone to scratching when handled.

There is something to be said about dealing with a reputable dealer that you can trust versus some place you have no knowledge and personal experience with.

Also depends on what your reasoning behind the purchase.

Investment, speculation, or transport of value to what follows down the road. 

Do your own homework and do what your comfortable with.

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